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MODERN  AMERICAN  METHODS 


OF 


S.  B.  CHRIST\ 


COPPEE  SMELTING 


BY 

EDWARD  D.  PETERS,  JR.,  M.E.,  M.D. 

MEMBER  OF  AM.  INST.  OF  MINING  ENGINEERS,  FORMER  GOV'T  ASSAYEH  OF  COLORADO,  LATE  SUP'T 

OF  OHFOHD  COPPER  AND  SULPHUR  Co.;  PARROT  SILVER  AND  COPPER  Co.;  LATE 

CONSULTING  METALLURGIST  OF  CALUMET  AND  HECLA 

COPPER  Co.,  VERMONT  COPPER  Co.,  ETC. 


NEW  YORK 

SCIENTIFIC  PUBLISHING  COMPANY 
27   PARK   PLACE 

1887 


TW78-0 


COPYRIGHT,  1887, 
BY  THE  SCIENTIFIC  PUBLISHING  COMPANY. 


.'•  ••*    •, 

f-  >'••  :  •::    :  -V- 
•  «•*•«•   •»«..<>*. 


DEDICATION 


TO  JAMES  DOUGLAS,  JK., 

WHOSE    ABILITY    AS    A    METALLURGIST 

IS  ONLY  EXCEEDED  BY  HIS  VALUE  AS  A  FBIEND, 

THIS    VOLUME    IS    AFFECTIONATELY    INSCRIBED    BY 

THE  AUTHOR. 


PREFACE. 


THE  collection  of  papers  which  forms  this  book  was  mostly 
prepared  in  moments  stolen  from  more  active  professional 
duties,  and  must  consequently  lack  the  uniformity  and  com- 
pleteness which  is  compatible  only  with  ample  leisure  and 
freedom  from  other  more  pressing  cares. 

It  has  been  my  intention  to  confine  myself  principally  to 
facts  gleaned  from  my  own  experience,  and  only  to  touch  upon 
theoretical  questions  when  essential  for  the  understanding  of 
practical  facts. 

As  the  items  of  cost,  both  of  construction  and  of  sub- 
sequent operation,  are  amongst  the  most  important  of  all  the 
practical  questions  that  face  the  originators  of  new  smelting 
enterprises,  and  as  these  are  virtually  unattainable  to  the  gen- 
eral public,  I  have  gone  into  these  figures  in  considerable  de- 
tail, not  calculating  expenses  as  they  appear  on  paper,  and  when 
everything  is  running  smoothly,  but  giving  the  actual  results 
of  building  on  a  large  scale,  and  of  smelting  many  thousand 
tons  of  ores  under  varying  circumstances,  and  in  all  of  the  or- 
dinary kinds  of  furnaces. 

Owing  to  the  magnitude  of  the  subject,  I  found  it  impos- 
sible to  touch  upon  the  so-called  "  Wet  Methods  "  without  in- 
creasing the  size  and  consequent  cost  of  this  volume  to  an  ex- 
tent that  might  probably  peril  its  circulation. 

The  author  desires  to  acknowledge  the  valuable  assistance 
of  Mr.  J.  E.  Mills,  in  connection  with  the  geology  of  the  Butte 
mining  district,  and  to  credit  Mr.  H.  M.  Howe  and  Mr.  A.  F. 
Wendt  with  the  use  he  has  made  of  their  papers  on  "  Copper 
Smelting  "  and  on  "  The  Pyrites  Deposits  of  the  Alleghanies." 

But,  above  all,  he  has  to  thank  Mr.  James  Douglas  for  a 
thorough  and  minute  revision  and  criticism  of  his  manuscript 
just  before  publication. 

E.  D.  P.,  JR. 

WALPOLE,  June,  1887. 


TABLE   OF  CONTENTS. 


CHAPTER  PAGE 

I.  DISTRIBUTION  OP  THE  ORES  OP  COPPER. 1 

n.  DESCRIPTION  OF  THE  ORES  OP  COPPER 11 

III.  METHODS  OP  COPPER  ASSAYING 16 

IV.  THE  ROASTING  OF  COPPER  ORES  IN  LUMP  FORM 37 

V.  STALL-BOASTING 82 

VL  KILN-ROASTING 109 

VII.  CALCINATION  OP  FINE  ORE  AND  MATTE 115 

VIII.  CHEMISTRY  OP  THE  CALCINING  PROCESS 157 

IX.  SMELTING  OF  COPPER 170 

X.  BLAST-FURNACES  OP  BRICK. 215 

XI.  BLAST-FURNACE  SMELTING 246 

XII.  REVERBERATORY  FURNACES 278 

XIII.  TREATMENT  OP  GOLD  AND  SILVER-BEARING  COPPER  ORES 327 

XIV.  BESSEMERIZING  COPPER  MATTES  . .  .330 


MODERN  AMERICAN  METHODS 


OF 


COFFEE  SMELTING. 


CHAPTEE  I. 

DISTBIBUTION  OF  THE   ORES  OF  COPPER. 

THE  ores  of  copper  are  widely  distributed  over  the  earth's 
surface,  and  may  be  found  in  almost  every  geological  forma- 
tion ;  but  the  deposits  of  commercial  importance  had  their  ori- 
gin, for  the  most  part,  at  a  very  early  period  of  the  world's 
history.  The  mines  of  the  old  world,  as  well  as  those  of  Chili 
and  Australia,  having  been  described  with  great  minuteness  by 
various  careful  authors,  there  remain  to  be  mentioned  in  this 
place  only  the  principal  copper  districts  of  North  America, 
which,  for  convenience  of  description,  may  be  classed  in  four 
groups : 

I.  The  Atlantic  coast  beds. 
II.  The  Lake  Superior  deposits. 

III.  The  Mountain  system  of  veins. 

IY.  The  Southern  Carbonate  deposits. 

I.   THE  ATLANTIC   COAST  BEDS. 

Throughout  its  whole  extent  in  North  America,  the  Atlantic 
coast  is  bordered  by  a  succession  of  parallel  ranges,  which,  by 
their  general  geological  as  well  as  geographical  analogy,  must 
be  classed  in  the  same  system.  They  form  an  unbroken  chain 
from  Florida  to  Labrador,  and  thence,  continuing  their  same 
northeasterly  direction  along  the  coast  of  that  bleak  country, 
dip  beneath  the  waters  of  Baffin's  Bay,  where  they  are  repre- 


2  MODEKN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

sented  by  a  series  of  submarine  peaks,  and,  nourishing  the  gi- 
gantic glacier  system  of  "Western  Greenland,*  terminate,  so  far 
as  known,  in  Mount  Edward  Parry,  north  latitude  82°  40'.  Dr. 
T.  Sterry  Hunt's  admirable  researches  have  given  us  a  very 
clear  insight  into  the  origin,  formation,  and  structure  of  this 
immense  range  of  mountains  within  the  confines  of  the  United 
States  and  Canada.  It  consists  essentially  of  metamorphic 
rocks — largely  crystalline  schists — and  is  metal-bearing  to  a 
greater  or  less  degree  throughout  its  entire  extent,  though  only 
in  a  few  places  is  copper  found  in  a  sufficiently  concentrated 
form  to  justify  any  attempts  at  extraction. 

The  only  copper  mineral  of  importance  in  this  range  is 
chalcopyrite.  In  the  more  northerly  division,  where  there  has 
been  extensive  glacial  denudation,  this  reaches  unaltered  almost, 
or  quite,  to  the  grass-roots,  while  from  Virginia  into  Tennessee, 
where  abrasion  has  not  taken  place,  and  where  oxidation  has 
been  assisted  by  climatic  influences,  decomposition  with  subse- 
quent concentration  is  found  to  a  considerable  depth.  The 
result  of  this  is  usually  a  zone,  rich  in  an  impure  black  oxide  of 
copper  containing  a  certain  proportion  of  sulphur,  which  some- 
times occurs  in  considerable  quantities  near  the  surface,  after 
first  passing  through  a  greater  or  less  extent  of  barren  iron 
oxide,  derived  from  pyrite,  and  which  has  no  doubt  furnished 
the  copper  to  enrich  the  underlying  zone. 

The  occurrence  of  this  valuable  mineral  in  merchantable 
quantities  has,  in  more  than  one  instance,  raised  expectations 
and  led  to  large  expenditures  that  have  subsequently  proved  en- 
tirely unwarranted ;  for  at  a  slightly  greater  depth,  the  unal- 
tered vein  assumes  its  true  character  of  a  more  or  less  solid 
pyrite  and  pyrrhotite,  carrying  a  very  small  amount  of  copper 
(seldom  above  three  per  cent.)  in  the  form  of  the  common  yel- 
low sulphuret.  When  the  accompanying  mineral  is  a  bisul- 
phide of  iron  and  the  locality  is  favorable,  the  pyrite  may  be 
utilized  in  the  manufacture  of  sulphuric  acid,  the  copper  being 
extracted  from  the  residues  by  well-known  methods ;  but  when 
the  prevailing  mineral  is  the  racwosulphide — magnetic  pyrites 
— there  can  be  no  question  of  profitable  working,  pyrrhotite 

*  See  Dr.  Kane's  Arctic  Expedition  for  soundings  taken  in  Baffin's  Bay ; 
also  Geology  of  Greenland's  mountains. 


DISTRIBUTION  OF  THE   ORES   OF   COPPER.  8 

being  absolutely  valueless  since  copperas  has  become  a  by- 
product of  fence-wire  making.  At  Capelton,  in  Canada,  at 
Ely,  Vermont,  and  at  one  or  two  points  in  Newfoundland,  cop- 
per pyrite  occurs  in  a  sufficiently  concentrated  form  to  yield 
from  five  to  six  per  cent,  in  considerable  quantities,  an  ore  on 
which  profitable  operations  may  be  conducted,  under  favorable 
conditions. 

In  Virginia,  at  Ore  Knob,  North  Carolina,  at  the  Tal- 
lapoosa  mine,  in  Georgia,  and  at  Stone  Hill,  Alabama,  indica- 
tions of  a  similar  concentration  of  copper  have  given  rise  to 
extensive  explorations,  and,  in  some  cases,  to  the  expenditures 
of  large  amounts  of  money,  which  have  not  always  resulted 
satisfactorily.  These  are  all  examples  of  so-called  bedd,ed  veins, 
following  the  lines  of  stratification,  and  being  simply  sand- 
wiched in  between  the  layers  of  rock.  One  of  the  most  curious 
features  of  these  beds  is  the  alternate  occurrence  of  the  sul- 
phide of  iron  that  forms  the  great  mass  of  the  gangue,  as  pyr- 
rhotite  and  pyrite.  In  Capelton,  for  instance,  we  have  the  bi- 
sulphide ;  a  hundred  miles  distant,  at  Ely,  the  monosulphide 
alone  exists ;  in  Virginia  and  at  Ore  Knob,  the  monosulphide 
preponderates ;  while  in  the  Tallapoosa  mine,  the  bisulphide 
alone  is  found.  Neither  the  chemical  nor  geological  composi- 
tion of  the  corresponding  country-rock  explains  this  phenome- 
non. Here,  it  will  be  proper  to  mention  the  occurrence,  in 
stratified  rocks,  of  the  sulphide  of  copper  (copper  glance),  usu- 
ally in  unimportant  quantity,  throughout  Pennsylvania,  New 
Jersey,  and  other  Middle  and  Southern  States. 

Aside  from  a  number  of  shipments  of  from  ten  to  fifteen  per 
cent,  pyritous  ore  from  Newfoundland  to  England,  and  a  few 
hundred  tons  of  copper  produced  at  Strafford,  Vermont,  the 
only  important  contribution  that  this  group  furnished  to  the 
world's  metal  market  for  the  year  ended  1884  was  2,260,000 
pounds  from  the  Canadian  group  of  pyrites  beds.  A  few  tons 
of  this  metal  from  the  Maine  mines,  and  an  equally  insignifi- 
cant amount  from  certain  unimportant  private  enterprises, 
appear  to  complete  the  record  for  group  No.  I. 

In  1885,  the  Canadian  product  was  slightly  increased,  while 
the  Vermont  and  New  Hampshire  mines  greatly  diminished 
their  output. 


MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 


II.  THE  LAKE  SUPERIOR  DEPOSITS. 

These  have  excited  such  universal  interest,  from  their 
unique  character  and  their  great  commercial  importance,  that 
there  is  an  abundance  of  correct  and  detailed  information  con- 
cerning them  in  the  pages  of  the  Engineering  and  Mining  Jour- 
nal, the  United  States  geological  reports,  the  Transactions  of 
the  American  Institute  of  Mining  Engineers,  and  in  various  other 
publications  easily  accessible  to  the  student. 

The  grade  of  the  ore  furnished  by  these  extensive  conglom- 
erate deposits  is  very  low,  ranging  from  three-quarters  of  one 
per  cent,  of  copper  to  about  one  and  three-fourths  per  cent., 
save  in  the  case  of  the  Calumet  &  Hecla,  whose  extraordinary 
extent  and  richness — four  and  one  half  per  cent. — make  it  a  re- 
markable exception.  The  figures  just  mentioned  are  so  low  in 
comparison  with  the  percentage  of  many  less  profitable  sul- 
phuret  mines  that  it  is  necessary  to  explain  to  those  not  familiar 
with  the  subject,  that  the  occurrence  of  the  copper  in  the  Lake 
mines  in  a  native  or  metallic  state  permits  the  substitution  of 
an  inexpensive  mechanical  concentration  for  the  costly  series 
of  calcinations  and  fusions  necessary  in  the  treatment  of  sul- 
phide ores.  In  the  case  of  the  Lake  ores,  a  single  crushing  and 
washing  removes  the  gangue  rock  almost  completely,  leaving 
the  metal  in  such  a  condition  that  a  single  refining  process  fits 
it  for  use,  and  yields,  in  the  absence  of  sulphur,  arsenic,  or 
other  impurities,  a  copper  of  the  best  quality,  which  commands 
the  highest  price  in  the  market. 

The  production  of  this  group  of  mines  is  very  large,  and 
shows  a  steady  increase.  For  the  year  ended  December  31, 
1884,  it  aggregated  69,353,232  pounds  of  pure  copper,  which 
in  1885  was  increased  to  72,148,172  pounds,  while  the  striking 
of  the  Calumet  &  Hecla  vein  at  a  great  depth  by  the  Tamarack 
Company  promises  an  important  addition  in  the  future  to 
these  already  large  figures. 

While  speaking  of  the  distribution  of  copper  in  a  metallic 
form,  it  seems  best  also  to  include  the  native  copper  deposits 
of  Santa  Kita,  New  Mexico,  which  differ  so  radically  from  the 
other  members  of  the  group  in  which  they  geographically  be- 
long that  they  must  be  regarded  as  unique. 


DISTRIBUTION  OF  THE   OEES   OF   COPPER.  5 

In  the  southwestern  corner  of  New  Mexico,  a  large  but 
ill-defined  tract  of  land  is  overlain  by  porphyry,  which,  although 
apparently  homogeneous,  is  in  reality  of  several  varieties,  only 
one  of  which  is  metal-bearing.  It  is  only  where  this  particu- 
lar formation  comes  to  the  surface  that  the  rock  is  found  heav- 
ily stained  with  the  salts  of  copper ;  and  on  being  followed 
beyond  the  limit  of  destructive  atmospheric  influences,  it 
carries  a  fair  but  very  variable  percentage  of  copper  in  sheets, 
nodules,  threads,  etc. 

The  most  striking  difference  between  these  deposits  and 
those  of  Lake  Superior  is  in  the  degree  of  decomposition  of 
their  metallic  contents.  In  the  Santa  Rita  deposits,  this  de- 
composition has  progressed  to  such  an  extent  as  to  have 
transformed  the  entire  nodule  of  metal  into  an  oxide  or  car- 
bonate, the  red  oxide — cuprite — greatly  predominating,  while 
the  two  carbonates  occur  chiefly  as  stains  and  films.  Even 
such  pieces  of  metal  as  seem  to  have  escaped  oxidation,  and  to 
have  retained  their  original  form  and  appearance,  are  found, 
on  close  examination,  to  consist  of  numerous  thin  plates  of 
metal,  separated  by  a  layer  of  oxide,  while  the  entire  mass  is 
so  thoroughly  decomposed  that  little  difficulty  is  experienced 
in  grinding  the  greater  proportion  of  it  into  a  powder. 

This  condition  of  the  ore  naturally  produces  a  most  unfor- 
tunate complication  in  the  subsequent  process  of  mechanical 
concentration,  and  leads  to  enormous  losses,  especially  when 
stamps  are  used  for  crushing  the  ore. 

HI.  THE  MOUNTAIN  SYSTEM  OF  VEINS. 

In  this  group  are  all  the  deposits  of  copper  occurring  in  the 
Rocky  Mountains  and  Sierra  Nevadas  north  of  the  great  car- 
bonate districts  of  Arizona  and  New  Mexico. 

It  is  an  uncertain  division,  geographically  speaking,  and 
unsatisfactory  geologically,  as  it  contains  a  heterogeneous  col- 
lection of  mines  and  minerals,  scattered  over  an  immense  and 
ill-defined  tract  of  country.  An  enumeration  and  very  brief 
notice  of  the  few  great  centers  of  commercial  importance  will 
also  include  a  sufficient  diversity  of  ores  to  serve  as  types  for 
the  whole. 


6          MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

Most  northerly,  and  by  far  the  most  important  of  all,  are 
the  deposits  at  Butte  City,  Montana.*  The  copper  minerals 
occur  here  in  a  granite  formation,  in  some  places  approaching 
gneiss  in  structure  and  appearance.  The  veins  are  undoubt- 
edly true  fissures,  and  constitute  two  groups  of  different  geo- 
logical periods,  crossing  eacli  other  at  an  angle  of  about  60 
degrees,  although  no  exploration  has  been  done  at  the  points 
of  intersection.  The  east  and  west  veins  have  been  explored 
to  a  much  greater  extent  than  those  of  the  other  group,  and 
are  apparently  of  much  greater  value.  They  are  of  unusual 
width,  from  5  to  40  feet,  perhaps  averaging  7  feet,  and  vary 
greatly  in  pitch,  although  usually  approaching  the  vertical. 
They  seem  to  stand  in  some  constant  relation  to  an  accom- 
panying band  of  a  decomposed  material  resembling  porphyry, 
varying  in  width  from  100  to  1,000  feet,  and  near  the  longi- 
tudinal axis  of  which  they  are  situated. 

The  east  and  west  veins  are  alone  worthy  of  particular 
notice  in  this  place.  They  vary  among  themselves  in  the  min- 
erals that  constitute  their  value.  The  Anaconda  and  neighbor- 
ing properties  carry  in  the  decomposed  zone  chiefly  a  copper 
glance  of  greater  or  less  purity,  while  the  great  Parrot  vein, 
with  its  satellites,  yields  principally  an  ore  resembling  bornite 
(peacock,  or  horseflesh  ore),  which  varies  greatly  in  its  chemical 
composition.  A  striking  feature  of  these  veins  is,  that  they 
carry  little  or  no  copper  for  a  space  of  from  50  to  500  feet  (aver- 
age about  250  feet)  from  the  surface  down  to  water-level,  when 
the  rich  minerals  already  described  appear  suddenly,  chang- 
ing from  poverty  to  wealth  in  the  space  of  a  few  feet, 
instead  of  gradually,  as  is  usually  the  case  in  other  dis- 
tricts. 

This  rich  zone  has  evidently  derived  its  principal  value 
from  the  leaching  out  of  the  surface  portion  of  the  vein,  and 
its  unusual  extent  may  be  inferred  from  the  fact  that  many  of 
the  workings  have  penetrated  it  for  300  feet  or  more,  without 
finding  any  serious  diminution  in  its  copper  contents ;  but 

*  For  a  detailed  description  of  the  mines  and  metallurgical  works  of  this 
district,  see  a  paper  by  the  author,  entitled  "  The  Mines  and  Reduction-Works 
of  Butte  City,  Montana."  United  States  Geological  Survey,  Mineral  Resources, 
Albert  Williams,  Jr.,  1885. 


DISTRIBUTION   OF  THE   ORES   OF   COPPER.  7 

some  of  the  large  mines  have  already  worked  through  it  into 
the  unaltered  ore  of  corresponding  low  grade.* 

The  average  value  of  the  second-class  Butte  ore,  as  extracted, 
is  about  10  per  cent.,  and  perhaps  one  ton  in  ten  is  set  aside 
as  first-class,  averaging  30  per  cent.  The  second-class  ore  is 
well  suited  to  mechanical  concentration,  the  principal  draw- 
back being  the  accompanying  pyrite,  which,  though  valuable 
as  a  flux,  prevents  the  production  of  so  rich  a  concentrate  as 
economy  would  dictate,  and  adds  materially  to  the  expense  of 
calcination.  An  important  commercial  advantage  is  enjoyed 
by  the  owners  of  the  Butte  mines  in  the  silver  that  occurs  in 
amounts  varying  from  one  to  four  cents  for  each  pound  of 
copper.  Some  18,000  tons  of  such  ore,  smelted  under  the 
charge  of  the  author,  yielded,  according  to  the  assays  on  which 
the  product  was  sold,  0*5757  ounce  of  silver  to  each  per  cent, 
of  copper,  or  3J  cents  silver,  at  $1*10  per  ounce,  to  each  pound 
of  copper. 

An  almost  exactly  analogous  occurrence  of  these  rich  purple 
ores  gave  originally  that  great  impetus  to  mining  that  has  placed 
Chili,  up  to  a  recent  date,  at  the  head  of  the  copper-producing 
countries  of  the  world,  and  a  steady,  though  by  no  means  rapid, 
improvement  in  practice  and  apparatus  has  enabled  her  to 
maintain  her  output,  even  though  the  rich  altered  ores  have 
been  long  since  exhausted,  and  have  given  place  to  the 
7  or  8  per  cent,  pyritous  material  that  forms  the  normal 
filling  of  these  and  most  other  copper  veins.  The  complete 
disappearance  of  the  more  valuable  mineral  occurs  at  a  depth 
of  about  500  feet  in  the  deepest  Chilian  mine  on  record,  the 
Pique  mine. 

The  product  of  the  Butte  district  for  the  year  1884  is  closely 
estimated  at  41,500,000  pounds;  for  1885,  67,798,864  pounds. 

The  remainder  of  No.  III.  group  is  of  a  miscellaneous  char- 
acter, geologically,  mineralogically,  and  geographically. 

The  next  most  noteworthy  occurrence  of  copper  is  in  the 
fissure-veins  of  Gilpin  County,  Colorado,  which  traverse  a 
granite  formation,  and  are  principally  important  for  their  value 


*  The  writer  desires  to  acknowledge  the  assistance  of  Mr.  Jaines  E.  Mills 
in  preparing  his  brief  statement  of  the  geology  of  the  Butte  copper  mines. 


8  MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

in  the  precious  metals.  The  copper  contents  rarely  exceed 
1  per  cent,  of  all  the  ore  extracted,  or  5  per  cent,  when 
only  the  first-class  or  smelting  ore  is  considered.  The  gangue 
is  invariably  quartz  or  decomposed  feldspar,  and  the  metal  oc- 
curs almost  exclusively  as  chalcopyrite,  in  company  with  small 
quantities  of  zinc-blende,  galena,  various  antimonial  and 
arsenical  compounds,  and  a  much  larger  amount  of  pyrite. 

The  new  San  Juan  region  promises  to  add  a  considerable 
amount  of  copper  to  Colorado's  quota.  The  metal  occurs  there 
principally  as  a  constituent  of  argentiferous  tetrahedrite.  The 
statements  of  ore-buyers,  verified  by  personal  examination, 
show  an  average  tenor  of  about  3^  per  cent,  of  copper  for  the 
ordinary  ore  as  shipped  from  these  mines.  Their  silver  value 
varies  from  20  to  500 — average  about  60 — ounces  to  the  ton. 
A  limited  amount  of  copper  is  furnished  from  other  districts  of 
Colorado,  but  is  in  no  case  mined  in  sufficient  quantities  to  jus- 
tify an  independent  business  apart  from  the  precious  metals, 
which  almost  invariably  constitute  90  per  csnt.  or  more  of 
their  value,  as  expressed  by  the  price  received  for  the  ore  at 
smelting-works.  The  product,  therefore,  is  insignificant,  and, 
when  added  to  that  of  the  districts  already  noticed,  will  not 
raise  the  total  product  of  group  No.  III.  for  1884  to  much 
above  44,000,000  pounds. 

IV.  THE  SOUTHERN  CARBONATE  DEPOSITS. 

It  is  to  this  group  of  oxidized  ores  that  the  attention  and 
capital  of  business  men  were  principally  directed  a  few  years 
ago,  and  although  the  deposits  of  this  nature  are  almost  limit- 
less in  number,  and  the  labor  and  expense  of  producing  metal- 
lic copper  from  minerals  that  have  already  been  prepared  by 
nature  for  the  simple  fusion  that  is  alone  necessary  are  com- 
paratively slight,  the  high  expectations  formed  have  seldom 
been  realized.  The  unfavorable  character  of  the  country,  the 
scarcity  of  fuel  and  water,  the  expense  of  transportation,  the 
distance  from  central  authority,  and,  above  all,  the  eccentric 
and  uncertain  character  of  the  deposits,  have  brought  about 
this  result,  and  the  copper  market  has  been  overloaded,  and 
many  valuable  deposits  exhausted,  without  any  corresponding 
advantages  to  the  promoters. 


DISTRIBUTION   OF  THE   ORES   OF   COPPER.  9 

The  most  important  mines  of  this  division  are  all  situated 
in  Arizona  or  New  Mexico,  and  differ  too  much  in  their  char- 
acteristics to  permit  of  any  general  description. 

In  one  class  of  these  mines,  notably  the  Copper  Queen,  the 
copper  occurs  as  carbonates  and  oxides,  associated  with  oxide 
of  iron  and  ferruginous  clays,  filling  immense  caves  in  the  lime- 
stone. 

In  another  class  of  mines,  such  as  those  at  Clifton,  Arizona, 
the  bodies  of  oxidized  ores  are  irregularly  distributed  through 
beds  of  diorite,  the  occurrence  of  the  ore  beds  being  apparently 
determined  by  intercalated  masses  of  limestone,  which  have 
played  an  important  part  in  either  the  deposition  or  alteration 
of  the  copper,  or  in  both  processes.  The  ore-bodies,  although 
they  occur  within  certain  limits,  were  irregularly  distributed, 
and  are  of  very  variable  size,  and  the  alteration  has  not 
occurred  to  any  great  depth. 

Although  this  class  of  deposits  furnishes  a  certain  amount 
of  the  very  richest  ore  known  to  the  mineralogist,  in  the  shape 
of  streaks,  bunches,  and  even  considerable  aggregations  of  red 
oxide  and  the  two  carbonates  of  copper,  the  average  percent- 
age of  this  metal  contained  in  the  furnace  charges  of  the  most 
extensive  and  profitable  smelting  establishments  belonging  to 
this  group  is  not  high.  A  constant  yield  of  10  per  cent,  is 
considered  very  good,  and  the  dividends  afforded  by  certain  of 
these  properties,  laboring  under  the  disadvantages  of  expen- 
sive fuel,  transportation,  etc.,  result  principally  from  the  exceed- 
ingly simple  nature  of  the  process  employed  and  the  remark- 
ably favorable  composition  of  the  accompanying  gangue  rock. 
This  consists  usually  of  a  mixture  of  oxides  of  iron  and  man- 
ganese, with  calc-spar,  and  for,  the  most  part  contains  just 
about  the  proper  amount  of  silica  to  form,  with  the  constitu- 
ents just  mentioned,  an  easily  fusible  slag,  and  one  reasonably 
free  from  copper,  considering  the  unusual  practice  of  produc- 
ing metallic  copper  and  a  slag  to  be  thrown  away  at  the  first 
fusion.  In  cases  where  the  contents  in  silica  exceed  the  proper 
amount,  very  basic  ores,  containing  an  excess  of  the  oxides  of 
iron  and  manganese,  can  almost  always  be  procured  in  the  im- 
mediate neighborhood  ;  or,  in  default  of  this,  beds  of  quite  pure 
iron  ore  and  quarries  of  limestone  almost  perfectly  free  from 


10       MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

silica  are  nearly  always  close  at  hand.  The  great  purity  of  the 
metal  produced  is  also  a  highly  favorable  factor  in  estimating 
the  relative  advantages  of  this  group ;  for,  aside  from  bringing 
a  price  nearly  equal  to  Lake  copper,  it  is  always  sure  of  a  ready 
sale. 

The  product  of  this  group,  including  the  small  amount  re- 
ferred to  in  the  succeeding  paragraph,  as  coming  from  unclas- 
sified sources,  may  be  safely  estimated  for  the  year  1884  at 
24,000,000  pounds,  dropping  in  1885  to  22,706,000  pounds. 

A  considerable  number  of  mines  and  deposits  that  cannot 
be  consistently  brought  under  any  of  the  four  divisions  enu- 
merated still  exist ;  but  aside  from  certain  sulphureted  veins  in 
Nevada  County,  California,  which  are  interesting  chiefly  on 
account  of  the  method  employed  for  the  beneficiation  of  the 
ore — leaching  and  precipitation  in  revolving  barrels — and  the 
Walker  River  mines  in  Esmeralda  County,  Nevada,  but  few 
deposits  are  worthy  of  note.  The  Nacimiento  copper  quar- 
ries in  Central  New  Mexico,*  the  Oscura  copper-fields  in  the 
Oscura  Mountains,  New  Mexico, t  and  the  Great  Belt  copper 
deposits  in  Texas  present  certain  curious  and  interesting  fea- 
tures to  both  mineralogist  and  paleontologist.  The  metal  in 
each  place  occurs  in  the  shape  of  petrifacts  of  shells,  fishes,  and 
palm-leaves,  branches,  and  twigs — all  changed  completely  into 
an  impure  variety  of  copper  glance,  and  found  in  that  same 
Permian  formation  that  at  Mansfeld,  Germany,  and  in  the  Rus- 
sian Empire,  has  been,  and  still  is,  so  prolific  in  copper. 

*  See  pamphlet  by  F.  M.  F.  Cazin,  for  a  full  and  accurate  description  of 
these  mines,  and  estimate  of  their  value. 

f  See  a  paper  by  the  author  in  the  Engineering  and  Mining  Journal  of 
November  18,  1882,  for  report  on  these  properties  and  the  surrounding 
country. 


CHAPTER  II. 

DESCRIPTION  OF  THE  ORES  OF  COPPER. 

ALTHOUGH  the  copper-bearing  minerals  are  numerous,  yet 
those  of  commercial  importance  are  few  in  number,  and  for  the 
most  part  quite  simple  in  chemical  composition.  The  following 
minerals  may  be  properly  considered  ores  of  copper,  and  are 
found  in  the  United  States  in  the  localities  enumerated. 

NATIVE  METALLIC  COPPER. 

Aside  from  the  extensive  occurrence  of  this  metal  in  the 
Lake  Superior  region  and  at  Santa  Rita,  New  Mexico,  it  is 
found  very  frequently  as  a  product  of  decomposition,  though 
seldom  in  sufficient  quantities  to  render  it  of  any  commercial 
importance.  It  is  usually  remarkable  for  its  purity. 

CUPRITE,  OR  RED  OXIDE  OF  COPPER,  Cu2O ;  88'8  Cu,  11-2  O. 

This  mineral  occurs  solely  as  a  product  of  decomposition, 
and  while  quite  widely  distributed,  is  nowhere  an  ore  of  any 
importance,  except  in  the  Southwestern  carbonate  mines, 
where  it  sometimes  permeates  large  masses  of  iron  oxide,  not- 
ably increasing  their  copper  contents.  Quite  large  lumps  of 
this  mineral  are  found  in  the  Santa  Rita  mines,  and  are  evi- 
dently the  result  of  an  oxidation  of  nodules  of  metallic  copper, 
the  unaltered  center  being  usually  preserved  of  greater  or  less 
size.*  Many  of  the  Butte  City  veins,  as  well  as  fissures 

*  An  average  sample  of  thirteen  tons  of  concentrates,  taken  by  the  author 
at  Santa  Rita,  in  1881,  and  partially  analyzed  under  his  supervision,  gave, 
after  continuing  the  concentration  by  hand  to  almost  complete  removal  of 
the  rock  constituents  : 

Oxides  of  copper 13'42 

Carbonates  of  copper 1'27 

Oxides  of  iron 0*13 

Metallic  iron  (from  stamps) 0*29 

Sulphur 0-11 

Insoluble  residue 0'37 

Metallic  copper 83*66 

Zn,  Ag,  Co,  Ni,  Pb,  Mn Traces 

99-25 
This  analysis  presented  points  of  considerable  difficulty,  especially  in  deter- 


12        MODEKN  AMERICAN  METHODS   OF   COPPEE  SMELTING. 

throughout  the  Eastern  Coast  Range  carry  this  mineral  in  their 

upper  portions  as  a  product  of  the  decomposition  of  sulphide 

ores. 

MELACONITE,  BLACK  OXIDE  OF  COPPER,  Cu02;  79-8  Cu,  20-2  O. 

This  ore,  with  its  metallic  contents  usually  in  part  replaced 
by  oxides  of  iron  and  manganese,  is  not  quite  so  widely  dis- 
tributed as  the  sub-oxide,  but  is  more  frequently  found  in 
masses  sufficiently  large  to  pay  for  extraction.  Its  most  re- 
markable occurrence  in  the  United  States  was  in  the  Blue 
Eidge  mines  of  Tennessee,  North  Carolina,  and  Virginia,  where 
the  upper  portion  of  the  beds  furnished  a  very  large  amount 
of  from  20  to  50  per  cent,  of  ore,  having  the  appearance  of 
melaconite,  and  giving  rise  to  expectations  that  were  always 
shattered  after  passing  through  this  rich  zone  and  reaching 
the  lean,  unaltered  pyrites  below.  This  so-called  black  oxide 
of  the  Blue  Eidge  *  region  seems  to  be  an  intimate  mixture  of 
glance,  oxide,  carbonate,  and  sometimes  finely  divided  native 
copper.  Two  analyses,  by  Dr.  A.  Trippel,  show  their  constitu- 
ents : 

Oxide  of  copper 5 '  75 

Sesquioxide  of  iron .'    1'50 

Sulphur 18-75 

Copper 71-91 

Iron -93 

Soluble  sulphates  of  copper  and  iron *72 

99-56  99-17 

A  pile  of  such  ore,  laid  on  a  bed  of  cordwood  and  moistened, 
often  ignites  the  wood  below,  and  thus  roasts  itself  without 
firing. 

MALACHITE,  Cu20,  CO2  +  HO;  71-9  CuO,  19-9  CO2>  8-2  HO. 

This  is  a  much  more  valuable  compound  of  copper  than 
the  two  preceding  oxides,  from  a  commercial  standpoint; 
although  no  mines  in  the  United  States  furnish  malachite  of 
sufficient  purity  to  fit  it  for  ornamental  purposes. 

mining  the  amount  of  oxide  of  copper  in  the  presence  of  metallic  copper.  En- 
tirely satisfactory  results  were  not  obtained;  but  the  method  proposed  by  W. 
Hampe,  by  means  of  nitrate  of  silver,  yielded  the  only  figures  that  could  lay 
the  slightest  claims  to  accuracy. 

*  Pyrites  Deposits  of  the  Alleghanies,  by  A.  F.  Weudt. 


DESCRIPTION  OF  THE  OEES  OF  COPPER.         13 

While  it  may  be  said  to  occur  in  widely  distributed  but 
ordinarily  in  non-paying  quantities,  in  the  upper  decomposed 
regions  of  most  copper  deposits,  there  are  certain  localities  in 
which  it  forms  the  principal  ore  of  this  metal.  It  is  very  sel- 
dom found  in  a  state  of  purity,  but  is  mixed  with  various  salts 
of  lime  and  magnesia,  oxides  of  iron  and  manganese,  silica  in 
its  various  forms  of  quartz,  chalcedony,  flint,  chert,  and  jasper, 
and  when  seemingly  present  in  large  quantities,  it  often  forms 
only  worthless  incrustations,  or  merely  colors  green  nodules 
and  masses  of  valueless  material.  It  is  then  difficult,  and  in 
some  cases  impossible,  to  form  any  accurate  opinion  of  the 
tenor  of  the  ore  from  its  external  appearance. 

AZURITE,  2CuO,  CO2  +  HO ;  69«2  CuO,  25-6  CO2,  5-2  HO. 

This  mineral  requires  only  a  passing  notice.  It  is  distrib- 
uted in  the  same  manner  and  occurs  under  the  same  conditions 
as  its  sister  carbonate,  but  in  very  much  smaller  amounts.  It 
occurs  in  profitable  quantities  only  in  some  of  the  Southwestern 
mines.  Specimens  of  this  mineral  are  found  with  malachite 
and  calc-spar  in  the  Longfellow  mine,  exceeding  in  beauty  any- 
thing of  the  kind  that  is  known  elsewhere  in  the  United  States. 

CHALCOPYRITE,  Cu2S,  FE2S3;  34-4  Cu,  30-5  FE,  351  S. 

This  is  by  far  the  most  widely  distributed  ore  of  this  metal, 
and  furnishes  the  greater  proportion  of  the  world's  copper.  It 
occurs  principally  in  the  older  crystalline  rocks,  frequently 
accompanied  with  an  overwhelming  percentage  of  iron  pyrites, 
in  bedded  veins  in  Newfoundland,  in  Quebec,  Canada,  in  Ver- 
mont, Virginia,  Georgia,  Tennessee,  and  Alabama. 

The  value  of  copper-bearing  fissure-veins  below  the  limit  of 
surface  decomposition  is  nearly  always  due  to  this  mineral. 
In  some  localities  the  chalcopyrite  forms  with  pyrite  a  fine- 
grained mechanical  mixture,  varying  in  color  with  its  percent- 
age of  copper  from  deep  yellow  to  steel-gray.  This  substance 
is  easily  recognized  under  the  microscope  as  a  mechanical  mix- 
ture, and  not  a  chemical  compound.  In  most  of  the  carbonate 
mines  of  the  Southwest  that  have  attained  any  considerable 
depth,  chalcopyrite  is  already  becoming  apparent,  in  minute 
specks ;  and  it  is  highly  probable  that  the  altered  ores  near  the 


14:        MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

surface,  with  their  valuable  admixture  of  ferric  oxides,  are  all 
due  to  the  decomposition  of  this  mineral.  The  sulphureted 
fissure-veins  of  the  Kocky  Mountains  and  Sierra  Nevada  are 
seldom  free  from  this  mineral,  although  their  value  almost  in- 
variably depends  upon  their  precious  metal  contents.  The 
remarkable  purple  ores  and  copper  glance  of  Butte  City,  Mon- 
tana, have  already  in  several  mines  given  place  in  depth  to  the 
universal  yellow  sulphide. 

CHALCOCITE,  COPPER  GLANCE,  Cu2S ;  79-7  Cu,  2O3  S. 
This  ore  is  seldom  found  in  a  condition  of  perfect  purity, 
its  valuable  component  being  frequently  in  part  replaced  by 
iron  and  other  metals.  Its  copper  percentage  rarely  falls  be- 
low 55,  and  even  at  this  low  standard  the  mineral  retains  its 
physical  characteristics,  a  slight  diminution  in  its  luster  being 
the  principal  difference  observable.  When  high  in  copper,  it 
greatly  resembles  the  white  metal  of  the  smelter.  Chalcocite 
containing  from  60  to  74  per  cent,  of  copper  occurred  also  pure 
and  is  relied  on  in  the  noted  Anaconda  mine,  Butte,  Montana. 
Several  of  the  other  Butte  mines  carry  the  same  mineral,  al- 
though, as  they  approach  the  western  boundaries  of  the  dis- 
trict, it  gradually  passes  into  bornite  or  peacock  ore.  It  is  also 
an  important  ore  in  Arizona,  occurring  in  large  quantities  near 
Prescott  as  well  as  in  the  Coronado  and  other  Clifton  mines. 
In  New  Mexico,  it  constitutes  virtually  the  entire  value  of  the 
Nacimiento  and  Oscura  Permian  beds.  It  occurs  frequently 
in  Texas  in  the  Grand  Belt  mines,  and  is  the  principal  ore  of 
numerous  narrow  fissures  in  the  Middle  and  Atlantic  States. 
In  the  Orange  Mountains  of  New  Jersey,  examined  by  the 
author,  it  was  found  in  a  species  of  shale,  as  an  ore  of  the  fol- 
lowing composition  : 


Copper 75-20 

Iron 4-10 

Manganese 113 

Silver  (2 -37  ounces) O'Ol 

Gold..  ..Trace 


Sulphur 17-97 

Insoluble I'lO 

99-51 


BORNITE  OR  ERUBESCTTE,  3Cu2S,  FE2S3;  55-58  Cu,  16-36  FE, 

28-06  S. 

This  is  one  of  the  most  beautiful  of  the  su]phureted  ores  of 
copper,  being  characterized  in  its  fresh  condition  by  a  superb 


DESCRIPTION  OF  THE  ORES  OF  COPPER.         15 

purplish-brown  color,  which  soon  changes  on  exposure  to  the 
air  into  every  conceivable  hue,  from  a  golden  yellow  to  the 
deepest  indigo,  and  from  a  brilliant  green  to  a  royal  purple. 
The  mode  of  occurrence  of  this  mineral  and  its  limited  extent 
of  distribution  as  regards  depth  indubitably  stamp  it  as  a  pro- 
duct of  decomposition,  solution,  and  re-deposition  of  the  me- 
tallic portion  of  the  vein.  Like  copper  glance,  this  mineral  is 
far  from  uniform  in  its  composition,  varying  in  richness  from 
42  to  nearly  70  per  cent,  of  copper  without  entirely  losing  its 
characteristic  colors. 

TETRAHEDRITE,  GRAY  COPPER  ORE,  FAHLORE  (Cu2S,  FES,  ZN$, 
AaS,  PBS)4  (SB2S3,  As2  S3) ;  30-40  PER  CENT.  COPPER. 

Except  in  those  rare  and  highly  argentiferous  varieties  in 
which  the  copper  is  replaced  to  a  greater  or  less  extent  by  sil- 
ver, this  is  seldom  regarded  in  the  United  States  as  an  ore  of 
copper. 

Both  its  scarcity  and  its  obnoxious  components  (arsenic, 
antimony,  etc.)  prevent  its  use  as  a  source  of  copper  in  this 
country,  where  the  extreme  purity  of  our  ores  has  established 
such  a  high  standard  for  this  metal.  Only  the  most  favorable 
circumstances,  mineral ogical,  metallurgical,  and  commercial, 
would  render  the  working  of  non-argentiferous  fahlores  at  all 
practicable.  This  mineral  occurs  in  small  quantities  in  certain 
of  the  Butte  copper  mines,  rendering  their  product  slightly  in- 
ferior to  that  from  the  oxidized  ores  of  Arizona  or  the  pure 
sulphides  of  Yermont.  This  slight  disadvantage  is,  however, 
far  outweighed  by  their  contents  in  silver,  which  doubtless  owes 
its  presence  to  this  same  arsenical  mineral.  From  the  San 
Juan  region,  Colorado,  an  argentiferous  tetrahedrite  adds  a 
notable  quantity  to  the  production  of  the  United  States.  It 
appears  principally  as  matte  from  the  lead  furnaces,  and  as 
black  oxide  from  the  Argo  separating  works. 


CHAPTEB  III. 

METHODS  OF  COPPEB  ASSAYING. 

THE  first  step  usually  taken  in  the  treatment  of  an  ore  of 
copper  is  to  learn  its  value  by  determining  the  proportion  of 
that  metal  that  it  contains.  This  process  is  called  assaying,  as 
distinguished  from  chemical  analysis,  which  includes  the 
further  investigation  as  to  the  general  composition  of  the 
ore. 

We  shall  confine  our  discussion  in  this  place  to  assaying 
only.  The  assaying  of  any  given  parcel  of  ore  is  necessarily 
preceded  by  the  process  of  sampling,  by  which  we  seek  to  ob- 
tain, within  the  compass  of  a  few  ounces,  a  correct  representa- 
tive of  the  entire  quantity  of  ore,  which  may  vary  in  amount 
from  a  few  pounds  to  several  thousand  tons.  As  a  rule,  it  will 
lessen  the  chance  of  serious  error  in  very  large  transactions,  to 
divide  the  lot  into  parcels  of  not  over  fifty  tons  each,  and 
sample  each  of  these  lots  by  itself. 

The  utmost  care  and  vigilance  in  sampling  and  assaying 
should  be  required  at  every  smelting- works,  both  in  the  interest 
of  the  works  and  in  that  of  the  ore-seller. 

Until  quite  recently,  it  has  been  customary  to  sample  lots 
of  ore  by  quartering  them  down,  rejecting  a  certain  proportional 
part  at  each  successive  operation,  and  reducing  the  size  of  the 
ore  fragments  as  the  quantity  to  operate  on  diminishes.  This 
is  a  laborious  and  expensive  method,  and  in  the  case  of  finely 
pulverized  ores,  may  well  be  replaced  by  the  use  of  the  "  split 
shovel,"  or  one  of  the  many  automatic  sampling  machines  that 
have  been  invented. 

But  since  the  establishment  of  public  sampling  works  at 
most  of  our  great  mining  centers,  where  the  correctness  of  the 
sample  is  guaranteed  by  the  works,  which  distribute  packages 
of  each  lot  of  ore  to  the  agents  of  the  various  rival  smelting 
companies,  for  them  to  assay  and  bid  upon,  the  vast  quantities 


METHODS   OF   COPPER  ASSAYING.  17 

of  ores  handled,  and  the  importance  in  many  instances  of  re- 
taining the  lump  form  of  the  ore,  as  essential  to  the  subsequent 
metallurgical  operations,  have  imperatively  demanded  some 
method  of  automatic  sampling  that  shall  be  rapid,  accurate,  and 
equally  applicable  to  ores  in  both  the  pulverized  and  lump  form. 

The  means  hitherto  employed  all  depend  upon  the  same 
general  principle  of  cutting  or  dividing  a  falling  stream  of  ore 
by  means  of  flanges,  fingers,  or  traveling  buckets,  in  such  a 
manner  as  to  obtain  a  certain  desired  proportion  of  it  for  a 
sample. 

While  many  of  these  devices  work  admirably  upon  pul- 
verized ore,  free  from  dampness  or  foreign  obstructing  sub- 
stances, they  are  apt  to  give  entirely  unsatisfactory  results  upon 
a  mixture  of  fine  and  coarse  ores,  while  the  presence  of  strings, 
chips,  rags,  etc.,  usually  clogs  them  and  deranges  their  working. 

Mr.  D.  W.  Brunton,  of  Denver,  Colorado,  whose  paper  I 
have  freely  used,  has  invented  an  automatic  sampling-machine 
that  is  apparently  free  from  all  the  defects  enumerated,  and 
which  has  been  shown  by  practical  trial  to  be  equally  applicable 
to  coarse,  fine,  or  mixed  ores,  while  it  cannot  be  clogged  by 
foreign  bodies  of  any  reasonable  size.* 

Brunton  overcomes  these  difficulties  by  deflecting  the  entire 
ore-stream  to  the  right  or  left,  while  falling  through  a  vertical 
or  inclined  spout.  By  a  simple  arrangement  of  movable  pegs, 
in  connection  with  the  driving  gear,  the  proportion  of  the  ore- 
stream  thus  deflected  into  the  sample-bin  may  vary  from  10  to 
50  per  cent. ;  the  latter  amount  only  being  required  in  coarse 
ores  of  enormous  and  very  variable  rich  ness,  while  for  ordinary 
lump  ores,  from  10  to  20  per  cent,  is  the  -maximum  required. 

Instead  of  passing  the  sample-stream  of  ore  into  a  bin,  this 
system  may  be  still  further  perfected  by  leading  it  directly  to 
a  pair  of  moderately  fine  rolls,  the  product  of  which  is  elevated 
to  a  second  similar  sampling-machine,  from  which  the  final 
sample  drops  into  a  locked  bin. 

Six  months'  constant  experience  with  this  sampler  has 
shown  that  10  per  cent,  of  20  per  cent.,  or  2  per  cent,  of  the 


*  See  Transactions  of  the  American  Institute  of  Mining  Engineers,  Vol. 
xiii.,  page  639,  for  drawings  and  full  description  of  this  sampler. 
2 


18        MODERN  AMERICAN"  METHODS   OF  COPPER  SMELTING. 

original  ore-parcel,  is  usually  quite  sufficient ;  though  in  ex- 
ceptional cases,  15  per  cent,  of  30  per  cent.,  or  4J  per  cent,  of 
the  ore,  may  be  required. 

The  two  machines  are  driven  at  different  speeds,  to  prevent 
any  possible  error  that  might  arise  from  isochronal  motion,  and 
by  careful  tests  of  this  machine  in  resampling  lots  of  ore,  the 
limit  of  error  has  been  found  less  than  one-fourth  of  one  per 


BRUNTON  S   SAMPLER. 


cent. ;  while  even  the  best  hand-sampling  may  vary  two  per 
cent. 

The  fact  that  the  division  is  one  of  time  and  not  of  ore  is 
one  of  the  most  important  features  of  this  valuable  invention, 
as  it  consequently  is  forced  to  deflect  the  exact  proportion 
of  the  ore-stream  for  which  it  is  set ;  whether  coarse  or  fine, 
wet  or  dry,  light  or  heavy. 

The  determination  of  the  moisture  present  in  any  given 
parcel  of  ore  is  also  a  matter  of  much  importance ;  and 


METHODS   OF   COPPER  ASSAYING.  19 

probably  more  inaccuracies  attend  this  apparently  simple  pro- 
cess than  any  other  of  the  preliminary  operations. 

This  determination  must,  of  course,  take  place  as  nearly  as 
possible  at  the  same  time  that  the  entire  ore  parcel  is  weighed, 
as  otherwise  the  sample  may  lose  or  gain  moisture. 

In  lump  ores,  it  is  difficult  to  obtain  a  correct  sample,  even 
for  moisture,  without  some  preliminary  crushing,  and  to  save 
labor,  it  is  best  to  use  a  portion  of  the  regular  assay  sample  for 
this  purpose  ;  the  accurate  weighing  of  the  entire  ore  parcel  be- 
ing postponed  until  just  before  or  after  the  sampling,  and  the 
portion  reserved  for  the  moisture  determination  being  placed 
in  an  open  tin  vessel,  contained  in  a  covered  metal  case,  hav- 
ing an  inch  or  two  of  water  on  its  bottom,  in  which  the  sample 
tins  stand. 

From  one-fourth  to  one  half-pound  of  the  sample  is  usually 
weighed  out  for  this  determination,  and  dried  under  frequent 
stirring,  and  at  a  temperature  not  exceeding  212  degrees. 
While  it  is  always  important  to  keep  within  the  limit  of 
temperature  just  mentioned,  it  is  especially  the  case  with  cer- 
tain substances  which  oxidize  easily.  Among  these  are  finely 
divided  sulphides,  and  above  all,  the  pulverulent  copper 
cements  obtained  from  precipitating  copper  with  metallic  iron 
from  a  sulphate  solution. 

Such  a  sample,  containing  actually  5  \  per  cent,  of  moisture, 
showed  an  increase  of  weight  of  some  2  per  cent,  on  being  ex- 
posed for  thirty  minutes  to  a  temperature  of  about  235  degrees 
Fahr. 

Certain  samples  of  ore — especially  from  the  roasting  fur- 
nace— are  quite  hygroscopic,  and  attract  water  rapidly  after 
drying. 

In  such  cases,  the  precautions  used  in  analytical  work 
must  be  employed,  and  the  covered  sample  weighed  rapidly, 
in  an  atmosphere  kept  dry  by  the  use  of  strong  sulphuric 
acid. 

The  sampling  of  the  malleable  products  of  smelting,  such 
as  blister  copper,  metallic  bottoms,  ingots,  etc.,  can  only  be 
satisfactorily  effected  by  boring  a  hole  deeply  into  a  certain 
proportional  number  of  the  pieces  to  be  sampled. 

Where  such  work  is  only  exceptional,  an  ordinary  ratchet 


20        MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

hand- drill  will  answer,  but  in  most  cases,  a    half-inch  drill 
run  by  machinery  is  employed. 

The  chips  and  drillings  are  still  further  subdivided  by  scis- 
sors, and  as  even  then  it  is  difficult  to  obtain  an  absolutely  per- 
fect mixture,  it  is  best  to  weigh  out  and  dissolve  a  much  larger 
amount  than  is  usually  taken  for  assay,  taking  a  certain  pro- 
portion of  the  thoroughly  mixed  solution  for  the  final  deter- 
mination. 

The  various  means  employed  in  the  laboratory  for  the  deter- 
mination of  the  percentage  of  copper  in  any  substance  are  given 
in  the  standard  works  so  fully  and  clearly  that  a  mere  enu- 
meration of  the  four  methods  that  the  author  deems  necessary 
and  sufficient  for  the  assay  department  of  any  copper  works 
would  probably  suffice.  But  having  been  at  considerable 
pains  in  former  years  to  determine  the  causes  and  extent  of 
the  inaccuracies  inseparable  from  certain  of  these  methods, 
and  also  having  noticed  various  essential  precautions,  not  men- 
tioned in  the  text-books  on  this  subject,  the  author  has  in- 
troduced a  few  original  observations  where  they  seem  re- 
quired. 

The  four  methods  of  assay  that  are  quite  sufficient  for  any 
commercial  or  technical  laboratory,  and  yet  that  are  every 
one  essential  if  it  be  desired  to  fulfill  every  condition  to  the 
best  advantage,  are : 

I.  Titration  with  potassium  cyanide  (KCy.). 
II.  Precipitation  with  zinc  (or  iron). 

III.Golorimetric  determination. 

IY.  Electrolytic. 

To  these  may  be  properly  added  the  Lake  Superior  fire 
assay,  as  peculiarly  suited  to  its  local  conditions.  As  the 
Swansea  fire  assay  for  copper  is  described  in  every  English 
metallurgical  work,  and  as  the  reasons  for  its  adoption  in  this 
country  can  hardly  be  imagined,  it  is  omitted. 

I.   TITRATION  WITH  POTASSIUM  CYANIDE. 

This  well-known  and  rapid  method,  usually  called  "  The 
Cyanide  Assay,"  depends  upon  the  power  possessed  by  an 
aqueous  solution  of  potassium  cyanide  to  decolorize  an  am- 
moniacal  solution  of  a  copper  salt,  and  is,  under  proper  condi- 


METHODS   OF  COPPEK  ASSAYING.  21 

tions,  quite  accurate  enough  for  ordinary  purposes.  These 
conditions  are  as  follows  : 

The  use  of  measured  and  constant  amounts  of  acid  and 
ammonia. 

The  cooling  of  the  ammoniacal  copper  solution  to  nearly 
the  temperature  of  the  surrounding  atmosphere  before  titra- 
tion. 

The  intimate  mixture  of  the  cyanide  solution,  as  it  drops 
from  the  burette,  with  the  copper  solution,  and  a  sufficient, 
though  accurately  limited,  time  in  which  to  accomplish  its 
bleaching  action. 

The  establishment,  of  a  certain  fixed  shade  of  pink  at  the 
standardizing  of  the  cyanide  solution,  to  which  all  subsequent 
assays  must  be  as  closely  as  possible  approximated  in  color  for 
the  finishing  point.  This  renders  it  impossible  for  any  chemist 
to  work  with  another  person's  solution  until  he  has  first  stand- 
ardized it  himself,  and  determined  its  strength  according  to 
his  own  custom. 

The  absence  of  zinc,  arsenic,  and  antimony,  whose  presence 
has  long  been  known  to  seriously  vitiate  results,  though 
exactly  to  what  extent  has  never  been  demonstrated,  until  a 
series  of  experiments  on  this  point  was  carried  out  in  1882 
under  the  direction  of  the  author,  and  still  more  recently  by 
Torrey  &  Eaton. 

From  a  long  list  of  results,  some  of  them  even  contradictory, 
the  following  deductions  were  drawn : 

The  presence  of  zinc  in  quantities  below  4J  per  cent,  has 
no  perceptible  influence  on  results. 

Five  per  cent,  of  zinc,  in  a  siliceous  ore  of  copper,  contain- 
ing no  other  metals  except  iron,  caused  a  constant  error  on  the 
plus  side  of  about  0*22  per  cent.,  which  increased  in  a  toler- 
ably regular  ratio  with  an  increased  percentage  of  zinc. 

After  eliminating  a  few  results  that  varied  very  greatly  and 
unaccountably  from  all  others,  an  average  of  about  six  deter- 
minations of  each  sample  yielded  the  following  figures.  The 
ore  just  described  was  used  in  every  case,  and  the  zinc  added 
in  the  shape  of  a  carefully  determined  sulphide,  allowances 
being  also  made  for  the  increase  in  the  weight  of  the  ore 
sample  resulting  from  this  addition  of  foreign  matter. 


22        MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 


Ore  free  from  zinc,  11  '16  per  cent,  copper. 

No.  1  with    4  per  cent,  zinc,  11-46        " 


5 
6 

8 
10 
15 
20 


11-55 

11-72 

12-1 

13-2 

13-3 

13-9 

13-8 


The  presence  of  arsenic  and  antimony  in  much  smaller  pro- 
portions— 1  per  cent,  or  less— may  cause  errors  on  both  plus 
and  minus  sides  to  the  extent  of  one-half  a  per  cent,  or  more, 
and  in  larger  quantities  will  generally  render  the  test  totally 
unreliable. 

Another  important  and  oft-neglected  precaution  is  the  test- 
ing of  the  precipitate  of  hydrated  oxide  of  iron  caused  by  the 
addition  of  ammonia  to  the  original  solution.  This  bulky 
precipitate,  especially  in  the  case  of  mattes  and  highly  fer- 
ruginous ores,  may  retain  a  considerable  amount  of  copper 
which  even  the  most  careful  washing  will  not  remove,  but 
which  may  be  speedily  determined  by  dissolving  the  pre- 
cipitate in  the  smallest  possible  quantity  of  muriatic  acid, 
saturating  with  ammonia,  and  again  titrating  if  any  blue 
coloration  is  produced.  The  following  results,  taken  from  the 
note-book  of  an  experienced  chemist,  who  had  never  been 
aware  of  this  possible  source  of  error  until  accidentally  men- 
tioned to  him  by  an  assayer  in  the  employ  of  the  writer,  and 
who  at  once  instituted  careful  experiments  to  ascertain  the 
probable  extent  of  the  mistakes  that  he  had  made  while  acting 
as  assayer  to  large  smelting- works,  give  some  idea  of  the  serious 
discrepancies  that  may  arise  from  the  non-observance  of  this 
precaution : 

Without  resolution  of          With  resolution  of 
Character  of  sample.  precipitate.  precipitate. 

No.  1,  pyritous  ore 21 '2  per  cent,  copper    23'7  per  cent,  copper 


2,  bornite 37'8 

3,  cupola  matte 27'7 

4,  reverberator^  matte 46'4 

5,  blue  metal 57'7 

6,  white  metal 74'7 

7,  regule 86'2 

8,  blister  copper 97 '3 


42-4 
31-2 
47-4 
58-2 
75-2 
86-4 
97-2 


METHODS   OF   COPPER  ASSAYING.  23 

As  might  be  expected,  the  greatest  discrepancies  exist  in 
connection  with  those  samples  containing  the  largest  amounts 
of  iron,  and  decrease  to  nothing  as  the  iron  contents  diminish. 

In  the  absence  of  the  injurious  elements — zinc,  arsenic, 
antimony — the  cyanide  assay  is  sufficiently  accurate,  and, 
from  its  simplicity  and  rapidity  of  execution,  it  is  peculiarly 
adapted  to  the  daily  working  assays  from  the  mine,  smelter, 
and  concentrator.  In  fact,  it  is  the  mainstay  of  the  over- 
crowded metallurgical  assayer,  and  can  be  used  for  nearly 
every  purpose,  except  for  the  buying  and  selling  of  ores  and 
copper  products,  and  for  the  determination  of  very  minute 
quantities  of  copper  in  slags.  It  is  frequently  employed  with 
satisfaction  for  the  last-named  purpose,  a  much  larger  amount 
than  usual  being  taken,  in  order  to  obtain  a  solution  suffi- 
ciently rich  in  copper  to  exhibit  a  reasonable  degree  of  color. 

Messrs.  Torrey  &  Eaton  have  recently  published  additional 
investigations  of  great  value  on  the  effect  of  various  substances 
upon  the  accuracy  of  the  cyanide  method.  (See  Engineering 
and  Mining  Journal,  May  9th,  1885.) 

In  their  experiments,  they  employed  a  cyanide  solution 
capable  of  showing  one  thirtieth  of  one  per  cent,  of  copper,  and 
took  every  precaution  to  have  all  conditions  identical  during 
the  various  tests ;  all  solutions  titrated  being  of  the  same  de- 
gree of  strength. 

Silver  and  Bismuth. — A  solution  was  made  of  the  following 
metals : 

Copper -550  gram. 

Bismuth -200       " 

Silver -250       " 

The  silver  was  precipitated  with  hydrochloric  acid,  and 
ammonia  added  after  filtering  and  washing.  Two  titrations 
gave  : 

No.  1 54*90  per  cent,  copper 

No.  2 54-85        "  "        instead  of  55  per  cent. 

These  results  show  that  a  solution  containing  the  very  un- 
usual proportion  of  20  per  cent,  of  bismuth  and  25  per  cent, 
of  silver  can  be  titrated  to  within  O'l  per  cent,  of  its  value  in 
copper. 


24        MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

Lead. — This  metal,  being  a  common  element  in  copper  ores 
and  alloys,  was  introduced  into  a  copper  solution  in  the  follow- 
ing proportions : 

Copper '200  gram. 

Lead '800  ~    " 

After  adding  ammonia  and  allowing  the  lead  precipitate  to 
separate  for  two  or  three  hours,  it  was  titrated,  giving  2O28 
per  cent,  of  copper,  instead  of  20  per  cent.  Messrs.  Torrey  & 
Eaton,  therefore,  believe  that  the  amount  of  lead  commqnly 
present  in  ores — from  5  to  40  per  cent. — would  not  injuriously 
affect  the  operation. 

Arsenic. — Torrey  &  Eaton  titrated,  without  filtering,  a  solu- 
tion containing  '600  gram  arsenic,  '400  gram  copper,  finding 
39 -8  per  cent,  instead  of  40  per  cent.  Therefore  any  ordinary 
amount  of  arsenic — from  5  to  15  per  cent. — would  seem  to 
have  no  injurious  influence. 

Ammonia  and  hydrochloric  acid,  when  indiscriminately 
used,  were  found  by  Messrs.  Torrey  &  Eaton  to  cause  serious 
errors,  the  results  being  influenced  to  the  extent  of  from  J  to 
1  per  cent,  by  any  large  excess  of  either. 

Lime  in  large  quantity  was  found  to  confuse  results. 

Magnesia  had  no  effect  whatever. 

II.    PRECIPITATION   WITH  ZINC. 

This  is  simply  a  modification  of  the  well-known  Swedish 
method,  and  has  been  so  arranged  by  Kerl  (see  his  work  on 
assaying)  as  to  be  suitable  for  every  variety  of  ore  or  product, 
regardless  of  impurities.  In  fact,  its  chief  value  in  the  modern 
metallurgical  laboratory  is  to  take  the  place  of  the  cyanide 
method  in  those  cases  in  which  the  occurrence  of  deleterious 
substances  forbids  the  employment  of  the  latter. 

The  principal  drawback  to  this  method  of  assay  is  the  de- 
lay caused  by  the  precipitation,  and  the  drying  and  weighing 
of  this  precipitate,  whose  strong  hygroscopic  quality  renders 
the  latter  manipulation  tedious  and  frequently  inaccurate. 
This  can  be  easily  obviated  by  dissolving  this  precipitate,  now 
free  from  all  impurities,  and  determining  the  percentage  of 
copper  by  the  ordinary  cyanide  assay.  This  modification  can 
be  strongly  recommended. 


METHODS   OF   COPPEK  ASSAYING.  25 

III.  THE  COLORIMETRIC  DETERMINATION  OF  COPPER. 

This  is  reserved  almost  exclusively  for  the  determination 
of  minute  quantities  of  copper  contained  in  slags,  tailings  from 
concentration,  and  similar  products. 

Heine's  modification  of  this  method,  as  described  by  Kerl, 
is  perhaps  the  most  convenient,  and  with  proper  solutions  for 
comparison,  preserved  in  bottles  of  colorless  glass  and  of  ex- 
actly the  same  size,  yields  results  that  cannot  be  surpassed. 
It  is  seldom  employed  for  substances  containing  over  one  and 
one-half  per  cent,  of  copper,  and  may  be  relied  upon  to  show 
differences  of  T§~O  of  one  per  cent ;  results,  however,  depending 
largely  upon  the  skill  of  the  operator,  and  his  capacity  for  dis- 
criminating almost  invisible  shades  of  color. 

IV.  THE    ELECTROLYTIC   METHOD,  OR  BATTERY   ASSAY. 

This  is  suited  to  nearly  every  class  of  material  and  every 
percentage  of  copper,  from  the  highest  to  the  lowest,  and  owing 
to  its  ease  of  execution  and  extreme  accuracy,  has  already 
largely  supplanted  the  ordinary  analytic  methods,  and  bids  fair 
to  do  so  altogether  in  all  important  cases.  Among  those  assay- 
ers  who  do  not  yet  practice  it,  there  seems  to  be  an  impression 
that  it  is  difficult  of  execution,  and  in  several  cases  under  the 
author's  observation  it  has  been  abandoned  after  a  few  futile 
efforts.  In  these  instances  there  must  have  been  some  direct 
violation  of  the  laws  governing  the  generation  and  transmis- 
sion of  electricity — it  being  always  the  battery  that  was  com- 
plained of — and  as  a  similar  though  usually  much  more  exten- 
sive and  complicated  form  of  battery  is  under  the  charge  of 
every  telegraph  operator,  the  disappointed  assayer  should  feel 
encouraged  to  persist. 

Messrs.  Torrey  &  Eaton  have  also  investigated  the  effect 
of  various  substances  upon  the  battery  assay,  and  have  arrived 
at  the  following  results,  which  are  not  quite  so  favorable  as  the 
author's  experience  in  practice  has  been : 

"Silver,  when  present  in  any  considerable  proportion — from 
1  to  3  per  cent. — gives  too  high  a  result.  It  should  always  be 
removed  by  hydrochloric  acid. 

"Bismuth,  even  when  present  in  small  quantity — \  per  cent. 
— is  partly  or  wholly  precipitated  with  the  copper,  and  must 


26          MODEEN   AMEKICAN   METHODS   OF  COPPER  SMELTING. 

consequently  be  determined  analytically  in  the  deposit.  A 
solution  of  -970  gram  copper,  -030  gram  bismuth,  gave  97*9 
per  cent,  copper  instead  of  97  per  cent. 

"  Lead,  derived  from  the  resolution  of  sulphate  of  lead  (if 
present)  by  the  wash-water,  is  partially  precipitated  with  the 
copper.  This  applies  only  to  large  percentages  of  lead. 

"  Zinc  and  Nickel  do  not  interfere  in  quantities  up  to  30 
per  cent. 

"Arsenic  precipitates  partly  with  the  copper,  and  not  after  it, 
as  has  been  supposed.  It  gives  a  bright  deposit,  but  may  be 
found  in  considerable  quantity  in  the  precipitate,  before  the 
solution  is  free  from  copper.  Arfer  complete  precipitation  of 
the  copper,  therefore,  the  deposit  should  be  titrated  with  cya- 
nide of  potassium." 

BATTERY  ASSAY. 

The  following  apparatus  and  method  of  procedure  will  be 
found  convenient,  although  every  assayer  has  his  own  private 
variations : 

MATERIALS  AND  APPARATUS  FOR   THE  ASSAY  ITSELF. 

Nitric  acid,  C.  P.  Glass  funnel  and  filters. 

Muriatic  acid,  C.  P.  Sand-bath. 

Distilled  water.  A  weighing-in  balance. 

Strong  alcohol.  An  analytical  balance. 
Small  beaker,  6-ounce. 

MATERIALS  AND  APPARATUS  FOR  THE  BATTERY. 

Copper  vitriol  of  best  quality.  Platinum  capsule  to  hold  sola- 
Two  one-gallon  gravity  cells,  with  tion,    about    2|    inches    in 

zinc  and  copper  elements  com-  diameter. 

plete  ;  also  connecting  couplers,  Heavy    platinum    wire,   bent 

insulated  wire,  etc.  into  a  spiral. 
Wooden  stand,  with  brass  ring 

for  supporting  capsule. 

When  weighing  out  the  substance  to  be  assayed,  sufficient 
of  the  same  should  be  taken  to  yield  about  150  milligrams  of 
pure  copper.  Thus,  in  treating  a  60  per  cent,  matte,  the  chem- 
ist would  weigh  out  0*25  gram  ;  while  in  the  case  of  a  5  per  cent, 
ore,  three  grams  would  be  the  proper  quantity.  The  finely 
pulverized  material  is  dissolved  in  the  customary  manner, 


METHODS   OF   COPPEK  ASSAYING.  27 

using  the  smallest  possible  quantity  of  acids,  which  in  most 
instances  may  be  nitric  acid  alone.  In  cases  where  it  is  found 
necessary  to  use  muriatic  acid,  the  solution  should  be  evapo- 
rated until  the  volatile  acids  are  completely  driven  off,  and  the 
copper  present  brought  into  the  condition  of  a  sulphate,  by  the 
addition  of  a  very  few  drops  of  sulphuric  acid.  In  this  case, 
the  presence  of  chlorides  renders  this  determination  inaccu- 
rate, while  either  nitric  or  sulphuric  acid  will  give  satisfactory 
results  ;  for  it  has  been  thoroughly  demonstrated  that  the  old 
prejudice  against  precipitating  from  a  nitrate  solution  was  un- 
founded. After  slight  dilution  with  distilled  water,  the  liquid 
is  filtered  into  the  platinum  capsule,  and  the  washing  of  the 
residue  continued  until  this  little  vessel  is  nearly  filled.  This 
has  usually  a  capacity  of  about  60  c.  c.,  and  is  constructed  of 
the  thinnest  platinum  foil  that  has  sufficient  strength  to  permit 
handling  when  filled  with"  liquid.  The  capsule  containing  the 
solution  is  now  transferred  to  a  brass  ring  of  proper  form, 
made  to  slide  up  and  down  upon  a  standard  like  a  filter  stand, 
and  capable  of  easy  connection  with  one  of  the  wires  from  the 
battery.  The  battery  may  be  placed  in  a  distant  closet  or 
wherever  convenient,  the  wires  being  conducted  along  the 
walls  to  where  the  precipitation  is  to  take  place,  and  fastened 
in  position  with  little  hooks  or  staples.  The  capsule  being 
placed  in  its  supporting  ring,  a  stout  platinum  wire,  coiled  into 
a  horizontal  spiral,  and  supported  by  a  movable  clamp  fixed  to 
the  same  standard  on  which  the  ring  slides,  is  lowered  until 
the  entire  flat  coil  dips  below  the  surface  of  the  solution.  It 
is  clamped  fast  in  this  position,  and  its  free  extremity  is  con- 
nected by  means  of  a  little  brass  muff  to  the  second  battery 
wire,  thus  immediately  establishing  the  current.  The  spiral 
should  be  connected  with  the  copper,  or  positive  element  of 
the  battery,  while  the  capsule,  on  which  the  precipitation  is  to 
take  place,  connects  with  the  zinc,  or  negative  element. 

The  more  or  less  lively  generation  of  gas,  which  rises  in  mi- 
nute bubbles  to  the  surface  of  the  liquid,  as  well  as  the  rapidity 
with  which  the  film  of  copper  is  deposited  upon  the  interior 
of  the  platinum  vessel,  are  indications  by  which  the  strength 
of  the  current,  and  consequent  energy  of  the  process,  may  be 
judged.  About  eight  hours  is  the.  customary  time  for  an  as- 


28        MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

say,  it  being  found  convenient  to  connect  the  wires  with  the 
already  prepared  assay  in  the  evening.  A  drop  of  the  solution 
is  tested  the  following  morning  with  hydrogen-sulphide  water, 
and  it  can  be  instantly  seen  whether  the  process  is  completed 
or  whether  some  additional  time  must  be  allowed.  If  this  test 
shows  the  solution  to  be  free  from  copper,  it  may  be  best  re- 
moved from  the  capsule  by  siphoning  off  with  a  tube  held  in 
one  hand  while  distilled  water  is  added  with  the  other  until 
the  washing  is  deemed  sufficient.  After  a  second  rinsing  with 
strong  alcohol,  the  capsule  is  dried  by  setting  fire  to  the  spirit 
that  still  adheres  to  the  surface,  after  pouring  off  all  that  will 
flow,  and  the  capsule,  with  its  adhering  plating  of  brilliant 
rose-red  copper,  is  weighed  on  an  analytical  balance.  The 
capsule  having  been  weighed  at  the  beginning  of  the  process, 
a  simple  subtraction  gives  the  amount  of  the  deposited  metal. 
The  result  is  not  affected  by  allowing  the  current  to  pass 
through  the  solution  for  hours  after  all  copper  is  thrown  down, 
unless  large  quantities  of  silver,  arsenic,  tellurium,  or  certain 
other  still  more  uncommon  substances  are  present.  In  such 
cases,  'the  copper  should  be  precipitated  by  the  Swedish 
method,  and  redissolved  in  a  few  drops  of  nitric  acid :  this 
will  give  a  solution  with  which  perfectly  accurate  results  can 
be  obtained  by  means  of  the  battery  assay.  A  brownish  dis- 
coloration, or  a  decided  diminution  in  the  beautiful  rosy  red 
of  the  electrolytic  precipitate,  is  not  uncommon,  and  usually 
leads  to  discarding  the  test ;  but  in  a  number  of  experimental 
cases,  it  was  found  that  such  discolorations  had  no  effect  on 
the  accuracy  of  the  result.  The  battery  for  this  assay  is  ex- 
ceedingly cheap,  and,  being  the  common  Callaud  or  gravity 
cell  that  is  used  by  the  telegraph  lines,  instructions  as  to  its 
management  can  be  obtained  from  the  nearest  operator.  The 
principal  precaution  necessary  is  perfect  cleanliness  and  great 
purity  of  the  Hue  vitriol  used.  The  mimber  of  cells  required 
for  any  given  number  of  assays  is  always  equal  to  the  number 
of  assays,  plus  one.  Thus,  while  a  single  assay  requires  two 
cells,  a  dozen  need  only  thirteen  cells,  which  can  be  so  coupled 
as  to  conduct  the  electric  current  through  the  entire  line  of 
solutions,  each  positive  being  always  connected  with  its  corre- 
sponding negative  element. 


METHODS   OF   COPPER  ASSAYING. 


29 


COST  OP  APPARATUS. 

Two  one-gallon  gravity  cells  complete,  with  5  pounds  CuSO4  and  wire 

connections $7.00 

Standard,  with  brass  fittings  and  other  connections 2.75 

Platinum  capsule,  30  grams,  at  45  cents 13.50 

Platinum  spiral,  5  grams,  at  35  cents 1.75 


Total $25. 00 

The  remaining  apparatus  necessary  consists  only  of  the 
ordinary  glass-ware,  balances,  etc.,  found  in  every  laboratory, 
and  the  foregoing  expense  can  be  reduced  some  $8  by  substi- 
tuting for  the  costly  capsule  a  thin  cylinder  of  platinum  foil, 
which,  being  connected  with  the  wire  from  the  zinc  element, 
is  suspended  in  the  solution,  which  is  contained  in  a  tall,  slen- 
der beaker,  the  spiral  in  its  turn  hanging  in  the  liquid  in  the 
center  of  the  cylinder.  The  only  valid  objections  to  this  assay 
are  the  expense  of  the  apparatus  and  the  slowness  of  the  pro- 
cess. Its  results,  when  executed  by  an  experienced  person, 
are  accurate  beyond  even  those  of  analytical  methods,  and 
arrived  at  with  infinitely  greater  ease  and  celerity.  The  fol- 
lowing figures  were  handed  the  author  by  a  friend  who  was 
desirous  of  testing  the  accuracy  of  this  assay,  and  who  made 
seven  determinations  of  the  same  sample  of  ore,  weighing  out 
different  quantities  in  each  case,  in  order  to  obtain  varying 
figures  in  the  calculation  of  the  percentage.  The  ore  was  all 
impure  tetrahedrite,  or  the  results  would  doubtless  have  been 
even  closer. 


No.  1 9'66  per  cent. 

2 9-67    "      " 

3 9-74    "      " 

4..  ..9-61    "      " 


No.  5 9-98  per  cent. 

6 9-85    "      " 

7 9'82    "      " 


It  is  evident  that  these  results  owe  their  remarkable 
uniformity  to  extreme  care  in  manipulation  and  the  employ- 
ment of  the  most  perfect  apparatus.  To  prevent  the  possibility 
of  any  precipitation  of  silver  in  assaying  argentiferous  sub- 
stances, a  few  drops  of  muriatic  acid  may  be  added,  and  as  the 
residue  left  upon  the  filter  will  then  contain  all  of  this  metal 
that  was  present,  it  may  be  at  once  tested  quantitatively  for 


30        MODERN  AMERICAN   METHODS   OF   COPPER  SMELTING. 

the  same,  either  by  the  scorification  or  crucible  method,  its 
freedom  from  copper  rendering  this  process  both  simple  and 
accurate. 

A  thorough  practical  familiarity  with  the  four  methods 
of  assaying  just  described  is  necessary  to  every  metallurgical 
chemist  who  hopes  to  do  his  work  with  satisfactory  accuracy. 

One  of  the  main  features  of  this  work  is  an  endeavor  to 
furnish  exact  estimates  of  the  cost  of  each  and  every  metal- 
lurgical operation.  The  cost  of  sampling  and  assaying  will 
vary  with  the  salaries  paid  to  assayers,  the  arrangements  for 
sampling,  etc.  But  in  order  to  furnish  some  kind  of  a  standard, 
the  cost  of  sampling  (exclusive  of  crushing,  which  is  a  necessary 
step  in  the  metallurgical  treatment)  and  assaying  has  been  care- 
fully footed  up  for  a  year  on  the  books  of  an  establishment 
partly  dependent  upon  custom  ore,  and  employing  a  single 
assayer  at  a  moderate  salary.  The  cost  per  ton  of  ore — which 
averaged  35  tons  per  day — was  37  cents  for  sampling  and 
18J-  cents  for  assaying. 

All  refuse  from  the  laboratory  that  can  possibly  contain 
copper,  as  well  as  specimens  brought  for  inspection — unless 
deemed  worthy  of  preservation — scrap  copper  and  brass,  old 
brass  screens,  and,  in  fact,  everything  containing  this  metal, 
should  be  collected  and  added  to  the  furnace  charge  from  time 
to  time,  taking  the  precaution  to  let  it  go  into  one  of  the 
earlier  operations,  that  the  arsenic,  antimony,  and  other 
deleterious  elements  certain  to  be  found  in  such  miscellaneous 
material  may  be  thoroughly  eliminated.  The  waste  copper 
solutions  produced  in  the  laboratory  should  not  be  thrown 
away,  but  emptied  into  a  cask  containing  a  few  hundredweight 
of  scrap-iron,  the  exhausted,  supernatant  liquor  being  siphoned 
off  when  necessary,  and  the  cement  copper  periodically  col- 
lected and  taken  to  the  furnaces.  Samples  of  ore,  matte,  etc., 
of  interest  only  to  the  establishment  itself,  should  be  preserved 
in  strong  brown  paper  parcels,  plainly  labeled,  and  systemati- 
cally stored  away.  Occasion  seldom  exists  for  keeping  them 
longer  than  from  three  to  six  months,  as  any  possible  suspi- 
cion or  accusation  of  error  on  the  assayer's  part  would  have 
been  either  investigated  or  completely  forgotten  within  that 
period. 


METHODS   OF   COPPER  ASSAYING.  31 

THE  LAKE    SUPERIOR  FIRE-ASSAY  FOR    ORES  FREE  FROM    SULPHUR 
AND   OTHER  METALLOIDS.* 

The  ordinary  English  fire-assay  has  been  so  frequently  de- 
scribed, and  is  so  little  suited  to  American  conditions,  that  it 
is  not  necessary  to  reproduce  it  here.  In  spite  of  the  difficulty 
of  its  execution  and  the  decided  and  constant  inaccuracy  in  its 
results,  it  is  so  interwoven  with  the  commercial  customs  of  the 
Swansea  copper  smelters,  and  its  replacement  by  one  of  the 
more  accurate  wet  methods  would  involve  such  a  revolution  in 
the  price-lists  and  methods  of  ore-buying,  that  it  is  likely  to 
maintain  its  sway  in  the  great  ore  market  of  the  world  for  an 
indefinite  time. 

The  Lake  Superior  fire-assay,  on  the  contrary,  is  not  only 
quick  and  inexpensive,  but  compares  favorably  in  accuracy 
with  the  best  wet  methods.  It  is  so  peculiarly  adapted  to  the 
conditions  that  have  given  it  birth  that  no  American  work  on 
the  metallurgy  of  copper  would  be  complete  without  a  detailed 
account  of  it,  especially  as  our  docimastic  literature  up  to  this 
time  has  made  little  mention  of  it.  In  the  Swansea  assay, 
the  substance  under  treatment  consists  usually  of  a  mixture  of 
sulphides  and  gangue-rock,  which  necessitates  a  series  of 
calcinations  and  fusions,  culminating  in  a  button  of  impure 
copper,  which  has  still  to  be  refined  at  a  considerable  loss. 
The  Lake  Superior  assayer  has  the  simpler  problem  of  dealing 
only  with  native  or  oxidized  compounds  of  copper  that  can  be 
reduced  to  the  metallic  state  at  so  low  a  temperature  as  to  pre- 
clude the  adulteration  of  the  copper  button  with  any  other 
metallic  substances,  and  thus  obviate  the  necessity  of  any 
refining  process.  In  spite  of  the  apparent  simplicity  of  this 
method,  it  demands  a  good  deal  of  skill  and  experience  to  ob- 
tain correct  results;  but  these  once  acquired,  no  assay  can 
excel  it  in  accuracy  and  celerity. 

A  glance  at  the  composition  of  the  substances  operated  on 
will  render  clear  the  objects  to  be  accomplished.  The  material 

*  The  author  takes  pleasure  in  acknowledging  his  indebtedness  to  Mr. 
Maurice  B.  Patch,  of  Houghton,  Michigan,  for  valuable  assistance  in  the 
preparation  of  this  section  on  the  Lake  Superior  assay.  The  position  held  by 
Mr.  Patch  as  chemist  to  the  Detroit  &  Lake  Superior  Copper  Company  is  a 
sufficient  guarantee  of  the  accuracy  of  the  following  description. 


32        MODERN  AMERICAN   METHODS   OF   COPPER  SMELTING. 

assayed  consists  of  the  concentrates  from  the  jigs,  tables, 
buddies,  and  other  concentrating  machines.  This  material  is 
technically  termed  "mineral,"  and  varies  greatly  in  richness, 
composition,  and  size  of  particles,  ranging  in  copper  from  10  to 
97  per  cent.,  and  in  some  instances  containing  a  gangue  of 
nearly  pure  ferric  oxide,  while  in  others  it  is  highly  siliceous. 
Nearly  all  grades  of  mineral  contain  a  considerable  proportion, 
from  3  to  10  per  cent.,  of  metallic  iron  from  the  stamp-heads, 
while  a  sample  containing  50  per  cent,  of  titanic  iron-sand  is  no 
unusual  occurrence.  It  can  readily  be  seen  that  no  small  skill 
is  required  so  to  flux  these  various  mixtures  as  to  obtain  a  clean 
and  fusible  slag,  and  a  button  of  copper  free  from  iron  or  other 
metals  that  may  be  reduced  with  comparative  ease,  and  thus 
yield  a  far  too  high  result. 

Sampling. — The  mineral  is  received  from  the  mines  packed 
in  strong  barrels,  weighing,  in  the  damp  condition  in  which  it 
arrives,  from  500  to  2,000  pounds,  its  weight  depending  on  its 
degree  of  concentration,  the  character  of  its  accompanying 
gangue,  etc.  As  this  material  is  to  be  refined  at  once,  the 
barrels  are  emptied  on  the  iron  plates  that  form  the  floor  in  the 
neighborhood  of  the  charging-door  of  the  refining-furnace. 
After  the  contents  of  each  barrel  have  been  thoroughly  and 
separately  mixed,  a  small  sample  is  taken  from  every  package, 
and  put  into.a  tightly  covered  copper  can.  Only  the  samples 
from  casks  of  the  same  grade  of  mineral  are  placed  in  any  one 
can,  as  each  quality  is  assayed  by  itself,  although  6  or  more 
different  grades  of  mineral  may  go  to  make  up  the  16  barrels 
that  usually  form  a  furnace  charge.  If  two  or  more  fur- 
naces are  simultaneously  in  operation,  the  samples  of  the  same 
grade  are  mixed  together,  to  avoid  the  unnecessary  multi- 
plication of  assays.  The  cans  containing  the  samples  are 
taken  to  a  safe  place,  and  deposited  in  a  box  divided  into 
separate  compartments,  and  containing  a  little  water  in  the 
bottom,  into  which  the  tight  copper  cans  are  set,  to  prevent  any 
loss  of  moisture  in  the  sample,  which  might  occur  despite  the 
close  cover. 

Fluxes. — Sodium  bicarbonate,  borax,  potassium  bitartrate 
(cream  of  tartar),  ferric  oxides,  sand,  and  slag  from  the  same 
operation  are  used  to  flux  the  gangue  and  other  worthless 


METHODS   OF   COPPER  ASSAYING.  33 

constituents,  and  effect  the  proper  reduction  of  the  copper. 
The  chief  impurity  to  be  dreaded  is  sulphur,  for  which  reason 
the  best  quality  of  sodium  bicarbonate  must  be  purchased,  and 
potassium  bitartrate  must  be  used  instead  of  argols.  The 
borax  and  soda  are  prepared  by  being  melted  in  iron  ladles,  to 
drive  off  their  water  of  crystallization,  and  then  pulverized 
through  a  twenty-mesh  screen.  Clean,  well-fused  slag  from 
former  operations  is  reduced  to  the  same  degree  of  fineness, 
while  the  oxide  of  iron  flux  is  prepared  by  pulverizing  selected 
fragments  of  specular  iron  through  a  fifty-mesh  sieve.  Any 
clean  quartz  sand  answers  for  the  silica  needed. 

Furnace. — A  common  natural  draught  melting-furnace  is 
used,  an  inside  measurement  of  9J  by  18  inches  being  large 
enough  to  accommodate  six  Hessian  crucibles.  These  are  set 
in  rows  of  three  on  two  thin  fire-bricks,  the  latter  resting  on  the 
longitudinal  grate-bars,  and  serving  to  raise  the  crucibles  to 
the  zone  of  greatest  heat.  Soft  coal,  broken  to  egg  size,  forms 
the  customary  fuel,  and  is  carefully  filled  in  around  the  charged 
crucibles,  which  are  not  placed  in  the  furnace  until  the  latter 
is  in  full  heat.  The  crucibles  employed  are  4  inches  high  and 
3  inches  in  diameter,  and  are  provided  with  well-fitting  covers 
made  at  the  works  from  a  mixture  of  fire-clay  and  sand ;  these 
are  the  more  necessary  because  the  assay  often  fills  the 
crucible  to  within  half  an  inch  of  the  top. 

The  skill  of  the  assayer  is  nowhere  more  evident  than  in 
the  fluxing  of  the  different  grades  of  mineral,  the  composition 
of  which  was  briefly  noticed  in  the  opening  paragraph  of  this 
chapter.  It  is,  of  course,  familiar  to  all  chemists  that  sodium 
bicarbonate  and  ferric  oxide  act  as  powerful  bases,  while  the 
electro-negative  elements  are  represented  by  borax  and  sand, 
the  potassium  bitartrate  exercises  a  strong  reducing  action,  as 
well  as  furnishing  an  active  base.  The  slag  equalizes  the 
entire  mixture,  being  capable  of  neutralizing  a  considerable 
amount  of  either  base  or  acid,  and  it  covers  the  molten  metal 
and  protects  it  from  oxidation.  It  is  not  to  his  skill  in  fluxing 
alone  that  the  assayer  trusts ;  of  almost  equal  importance  are 
the  degree  of  temperature  maintained  and  the  length  of  time 
that  the  assays  are  left  in  the  furnace. 

Good  results  can  only  be  obtained  by  shortening  the  period 
3 


34       MODEEN   AMEKICAN   METHODS   OF   COPPER  SMELTING. 


of  fusion  to  the  utmost.  This  demands  a  very  hot  furnace  at 
the  outset,  good  fuel,  and  a  lively  draught.  Under  these  con- 
ditions, an  easily  fusible  assay  will  probably  be  entirely 
finished  in  20  minutes,  while  from  25  to  30  minutes  are  re- 
quired for  difficult  samples.  It  is  quite  safe  to  assert  that,  if 
the  time  necessary  for  a  perfect  fusion  is  increased  to  40 
minutes,  the  resulting  button  will  contain  sufficient  impurities, 
reduced  from  the  slag,  to  give  a  result  from  2J  to  6  per  cent, 
too  high. 

This  assay  is  applicable  to  silicates  as  well  as  oxides  and 
native  copper,  and  the  results  obtained  from  the  assay  of  both 
refining  and  blast-furnace  slags  cannot  be  excelled  in  accuracy 
by  any  other  method. 

A  table  of  the  different  weights  of  fluxes  used  in  assaying 
the  various  grades  of  mineral  from  the  Peninsula  Copper 
Company's  works  is  annexed,  as  well  as  the  mixture  adopted 
for  reverberatory  slags  and  for  very  siliceous  ore  : 


MINERAL. 

Weight, 
grains. 

Borax, 
grains. 

Soda, 
grains. 

Slag, 
grains. 

Potassium 
bitartrate, 
grains. 

Sand, 
grains. 

Iron  ore, 
grains. 

Per  cent. 

Copper. 

No.  1 

92 

1,000 

60 

55 

200 

300 

. 

•  • 

2 

86 

1,000 

60 

60 

180 

300 

.  .  . 

. 

3 

60 

500 

100 

80 

300 

4 

33 

500 

150 

160 

300 

150 

5 

20 

500 

190 

200 

300 

175 

* 

35 

500 

140 

140 

300 

ioo 

t 

5  to  20 

500 

200 

200 

300 

... 

... 

The  percentage  of  slag-forming  materials  being  so  small  in 
Nos.  1  and  2,  it  requires  but  a  slight  amount  of  borax  and  soda 
to  flux  them,  while  an  addition  of  neutral  slag  is  necessary  to 
protect  the  molten  copper.  A  smaller  quantity  of  the  ore  is 
weighed  out  in  the  succeeding  assays,  as  they  are  so  poor  in 
copper  that  a  large  amount  of  flux  is  required  by  the  great 
quantity  of  gangue,  so  that  the  capacity  of  the  ordinary  cru- 
cibles would  be  greatly  exceeded  if  1,000  grains  were  used. 
No.  3  mineral  contains  just  sufficient  ferric  oxide  to  form  a 
good  slag  with  the  mixture  given ;  while  in  Nos.  4  and  5  this 
substance,  as  well  as  metallic  iron,  increases  to  such  an  extent 
as  to  require  the  addition  of  a  considerable  proportion  of  sand 

*  Calumet  &  Hecla  tail-house  mineral.        f  Ricli  slag  from  refining. 


METHODS   OF   COPPER  ASSAYING.  35 

to  flux  this  base  and  to  prevent  the  adulteration  of  the  button 
with  metallic  iron.  The  sample  of  Calumet  &  Hecla  tail-house 
mineral  given  is  typical  of  the  treatment  of  very  siliceous 
material.  There  is  nothing  remarkable  in  the  considerable 
proportion  of  borax  (an  acid  flux)  used  with  even  highly  quartz- 
ose  ores;  for  in  addition  to  the  fluxing  powers  of  the  soda 
that  it  contains,  a  boro-silicate  is  very  much  more  fusible  than 
a  simple-  silicate.  No  peculiarities  exist  in  the  execution  of 
this  assay ;  the  ore  and  fluxes  are  thoroughly  mixed  on  glazed 
paper,  and  covered  with  a  thin  layer  of  potassium  bitartrate 
after  being  poured  into  the  crucible.  In  the  No.  1  mineral, 
which  is  nearly  as  coarse  as  split  peas,  fragments  of  iron  fre- 
quently exist,  which  come  from  the  stamp-heads,  and  must  be 
picked  out  of  the  sample  after  weighing  out  for  assay;  not 
that  cast-iron  will  alloy  with  copper,  but  that  the  fragments 
will  be  found  imbedded  in  the  copper  button  after  cooling. 
The  grain  weights  are  used  instead  of  the  metric  system 
merely  from  habit,  and  because  neither  100  nor  50  grams  hap- 
pen to  be  convenient  quantities  for  assay,  the  former  being 
too  large  and  the  latter  too  small,  while  1 ,000  and  500  grains 
are  about  the  most  suitable  quantities,  as  determined  by  ex- 
perience. 

The  results  obtained  by  this  method  are  surprisingly 
accurate.  Duplicate  determinations  of  the  lower  grade 
samples  seldom  vary  more  than  O'l  or  0*2.  A  difference  of  0'4 
per  cent,  is  a  rare  occurrence,  even  in  the  higher  classes  of 
mineral  where  the  size  of  the  metallic  fragments  renders  the 
sampling,  and  even  the  weighing  out,  of  a  correct  assay  a  mat- 
ter of  some  uncertainty. 

A  few  results  from  Mr.  Patch's  notes  will  confirm  these 
statements.  An  average  series  of  tests  on  cupola  slags  by  the 
colorimetric  method  for  the  period  of  a  month,  duplicated  by 
the  fire-assay,  gave  a  result  0'05  per  cent,  lower  for  the  latter 
test,  the  slag  containing  about  0*5  of  one  per  cent. 

As  an  illustration  of  the  results  of  this  system  when  applied 
to  very  rich  ore,  a  comparative  test  was  made  for  eight  days 
on  No.  1  Calumet  &  Hecla  mineral,  with  the  following  results : 

Battery  assay ...  89'100  per  cent. 

Fire  assay 88'812   " 


36       MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 


A  similar  test  on  No.  2  Calumet  &  Hecla  mineral : 

Battery  assay 77'590  per  cent. 

Fire  assay 77'657  "     " 

A  similar  test  with  various  samples  : 


No. 
1.. 

2.. 
3.. 
4.. 
5., 
6.. 
7.. 
8.. 


Battery  assay. 


Mean  =  89 '544 


Mean  =  77-740 


Fire  assay. 

89-50 

89-60 
89-70 

*  Mean  =  89  92 

89-70 

77-40 

77-50 
77-70 

-Mean  =  77-50 

77-40 

It  is  a  somewhat  curious  fact  that  the  slight  loss  of  about 
0*25  per  cent,  of  copper,  which  results  from  the  passage  of  a 
minute  portion  of  the  metal  into  the  slag,  is  just  about  counter- 
balanced by  the  impurities  in  the  copper  button  from  the 
reduction  of  ferric  oxide,  the  amount  of  which  is  indicated  by 
the  following  analyses  of  copper  buttons — the  only  weighable 
impurity  being  iron : 


Copper, 
Per  cent. 
99-83 
99-84 
99-52 


Copper, 
Per  cent. 
99-76 
99-80 
99-46 


Copper, 
Per  cent. 
99-51 
99-87 
99-79 


This  account  of  a  little  known  process  will  doubtless  re- 
move the  impression  sometimes  held  by  chemists  that  the 
Lake  Superior  copper  assay  is  a  clumsy  and  imperfect  opera- 
tion, and  unworthy  any  advanced  system  of  metallurgy. 


CHAPTER  IV. 

THE   BOASTING  OF  COPPER  ORES  IN  LUMP  FORM.* 

BOASTING  or  calcination,  used  indiscriminately  in  the  lan- 
guage of  the  American  copper  smelter,  signifies  the  exposure 
of  ores  of  metals  containing  sulphur,  arsenic,  and  other  metal- 
loids to  a  comparatively  moderate  temperature,  with  the 
purpose  of  effecting  certain  chemical,  and  rarely  mechanical, 
changes  required  for  their  subsequent  treatment.  This  defini- 
tion is  restricted  to  the  dry  metallurgy  of  copper,  and  does  not 
take  into  consideration  chloridizing  roasting,  roasting  with 
sulphate  of  soda,  and  other  well-known  variations,  which  be- 
long either  to  the  metallurgy  of  the  precious  metals  or  to  the 
wet  treatment  of  copper  ores. 

The  care  and  attention  which  should  be  devoted  to  this 
preparatory  process  cannot  be  too  strongly  insisted  on,  nor 
can  any  one  carry  out  either  this  apparently  simple  roasting 
or  the  following  fusion  to  the  best  advantage,  who  is  not  thor- 
oughly familiar  with  the  striking  chemical  changes  that  in 
every  calcination  follow  closely  upon  each  other,  and  by  which 
the  sulphides  and  arsenides  of  the  metals  are  transformed  at 
will  into  a  succession  of  oxides,  subsulphates,  sulphates,  and 
subsulphides.  These,  reacting  upon  each  other  according  to 
fixed  and  well-known  laws,  enable  the  metallurgist  at  his  pleas- 
ure to  produce  every  grade  of  metal  from  black  copper  to  a 
low-grade  matte  that  shall  contain  nearly  all  the  metallic  con- 
tents of  the  ore  in  combination  with  sulphur.  To  avoid 
constant  repetition,  it  may  be  understood  that  in  speaking 
of  calcination,  when  sulphur  is  mentioned,  its  more  or  less 
constant  satellites,  arsenic  and  antimony,  are  also  included, 

*  In  English  metallurgical  literature,  the  term  roasting  is  applied  exclu- 
sively to  that  process  in  which  copper  matte  in  large  fragments  is  exposed  on 
the  hearth  of  a  reverheratory  furnace  to  an  oxidizing  atmosphere,  and  a  mod- 
erate, but  gradually  increasing,  temperature.  See  Matte  Concentration. 


88        MODERN   AMERICAN   METHODS   OF   COPPER  SMELTING. 

their  behavior  being  nearly  identical  under  ordinary  circum- 
stances. These  very  different  products,  as  well  as  the  amount 
of  ferrous  oxide,  the  most  important  basic  element  of  every 
copper  slag,  result  solely  from  the  degree  to  which  the  calcina- 
tion is  carried.  In  fact,  it  may  be  taken  as  literally  true,  that 
the  composition  of  both  the  valuable  and  waste  products  of  the 
fusion  of  any  sulphide  ore  of  copper  is  determined  irrevocably 
and  entirely  in  the  roasting-furnace  or  stall.  A  more  thorough 
study  of  the  reactions  just  referred  to  will  be  found  in  its  proper 
place.  Enough  has  here  been  said  not  only  to  explain  the  au- 
thor's object  in  devoting  so  much  attention  to  this  process, 
but  also  to  induce  such  metallurgists  as  are  not  already  thor- 
oughly familiar  with  the  theory  of  calcination  to  endeavor  to 
become  so  if  they  desire  to  ever  excel  in  the  economical  treat- 
ment of  sulphide  ores. 

The  varieties  of  calcination,  as  applied  to  the  dry  treat- 
ment of  copper  ores,  are  at  most  two  : 

1.  The  oxidizing  roasting,  which  is  necessarily  combined 
with  volatilization. 

2.  The  reducing  roasting,  limited  in  its  application  almost 
exclusively  to  substances  containing  much  antimony  or  arsenic. 

Plattner's  admirable  work  on  llostprocesse  contains  the 
whole  theoretical  part  of  calcination ;  but  a  foreign  language 
is  a  barrier  to  many  ardent  students  of  metallurgy,  and  his 
descriptions  and  plans  of  furnaces  and  apparatus  apply  to 
those  in  use  thirty  years  ago.  A  modern,  treatise  on  roastiog, 
regarding  the  subject  principally  from  a  practical  stand-point, 
and  adapted  to  present  American  conditions,  seems  desirable. 
Such  a  treatise,  however,  could  not  attain  the  highest  degree 
of  usefulness  without  a  consideration  of  the  theory  of  calcina- 
tion sufficient  to  enable  and  encourage  all  who  make  use  of  the 
more  practical  part  to  follow  with  ease  the  chemical  reactions 
on  which  the  process  is  based.  These  reactions  can  be  more 
easily  appreciated  and  remembered  after  first  becoming  famil- 
iar with  the  apparatus  and  means  by  which  the  exposure  of 
the  substances  under  treatment  to  the  influence  of  heat  and 
air  is  effected.  The  theoretical  discussion  will  be  postponed 
until  this  familiarity  is  attained. 

This  roasting  apparatus  must  vary  according  to  the  me- 


THE   BOASTING  OF  COPPER  ORES   IN   LUMP  FORM.  39 

chanical  condition  of  the  ore  under  treatment — that  is,  whether 
fine  or  coarse.  (See  article  by  the  author,  "  The  Boasting  of 
Copper  Ores  and  Furnace  Products."  United  States  Geologi- 
cal Survey \  Mineral  Resources  of  the  United  States,  Albert 
Williams,  Jr.,  1883.)  It  is  assumed  that  the  process  of  calci- 
nation, as  executed  in  the  dry  metallurgy  of  copper,  has  to 
deal  with  the  oxidizing  of  only  two  classes  of  material,  ores 
and  mattes.  The  appliances  for  the  roasting  of  these  sub- 
stances in  lump  form  may  be  divided  into  three  classes  : 

1.  Heap  roasting.     Suited  to  both  ore  and  matte. 

2.  Stall  roasting — 

a.  Open  stalls.     Suited  only  to  ore. 

b.  Covered  stalls.     Suited  to  both  ore  and  matte. 

3.  Kilns.     Suited  only  to  ore. 

The  mechanical  preparation  of  the  material  for  each  of 
these  three  forms  of  roasting  is  virtually  identical,  and  has  an 
important  influence  on  the  result  of  the  process.  The  size  to 
which  the  substance  under  treatment  should  be  broken  cannot 
be  arbitrarily  stated,  as  different  ores  vary  so  greatly  in  their 
composition  and  behavior.  Ores  containing  a  high  percentage 
of  sulphur — twenty-five  and  over — will  give  excellent  results 
if  so  broken  that  the  largest  fragments  shall  be  capable  of 
passing  through  a  ring  three  inches  in  diameter ;  while  more 
rocky  ore,  which  is  likely  to  be  of  a  harder  and  denser  texture, 
should  be  reduced  to  pass  a  two-inch  opening.  Careful  ex- 
periments can  alone  determine  the  most  profitable  size  for 
any  given  material,  and  should  be  continued  on  a  large  scale 
until  the  metallurgist  in  charge  has  fully  satisfied  himself  on 
this  point.  This  may  be  determined  with  the  least  trouble 
and  expense  by  noticing  the  weight  and  quality  of  the  matte 
obtained  by  smelting  the  roasted  ore  from  various  heaps 
formed  of  fragments  differing  in  their  maximum  size. 

All  other  conditions  being  identical,  the  heap  that  yields  the 
smallest  quantity  of  the  richest  matte  has,  of  course,  undergone 
the  most  perfect  oxidation,  and  should  be  selected  as  a  standard 
for  future  operations.  Variations  that  may  occur  in  the  chemi- 
cal or  mechanical  condition  of  the  ore  should  be  carefully 
watched  as  a  guide  in  fixing  upon  the  best  roasting  size.  Lo- 
cal conditions  must  determine  whether  a  jaw-crusher  or  hand 


40        MODERN   AMERICAN   METHODS   OF   COPPER  SMELTING. 

labor  should  be  used  for  this  purpose.  The  production  of 
fines  is  a  decided  evil  in  the  preparation  of  ore  for  heap  roast- 
ing, and  the  manual  method  possesses  a  certain  advantage  in 
this  respect,  though  this  consideration  may  be  outweighed  by 
other  economic  conditions.  A  trial  of  the  comparative  amount 
of  fines  produced  by  machine  and  hand-breaking  was  carried 
out  on  three  different  varieties  of  sulphureted  copper  ores  of 
average  hardness,  and  aggregating  2,220  tons.*  The  broken 
ore  was  thoroughly  screened ;  all  passiog  through  a  sieve  of 
three  meshes  to  the  inch  (6  mm.  openings)  was  designated  as 
fines. t  One  half  (1110  tons)  of  this  material  was  passed 
through  a  seven  by  ten  jaw  rock-breaker,  with  corrugated 
crushing-plates  (which  produce  a  decidedly  less  proportion  of 
fines  than  the  smooth  plates).  The  breaker  made  240  revolu- 
tions per  minute,  and  had  a  discharge  opening  of  two  and  one 
half  inches.  The  other  moiety  was  broken  by  experienced 
workmen,  with  proper  spalling-hammers,  into  fragments  of  a 
similar  maximum  size.  The  result  was  as  follows ;  only  the 
fine  product  being  weighed,  the  coarse  being  estimated  by  sub- 
tracting the  former  from  the  total  amount : 

Broken  by  Jaw-Crusher.  Tons.  Per  cent. 

Fine  product — below  6  nim.  in  diameter 192'25  17'32 

Coarse  product — between  6  mm.  and  64  mm 917  75  82  68 


Total 1,110-00  100-00 

Broken  by  Hand  Hammers. 

Fine  product — below  6  mm.  in  diameter 103 '34  9*31 

Coarse  product— between  6  mm.  and  64  mm.. .  .1,006  66  90'69 

Total 1,110-00  100-00 

These  results  are  quite  in  accordance  with  impressions  de- 
rived from  general  observation,  and,  as  will  be  noticed,  prove 

*  Unless  otherwise  indicated,  all  tons  equal  2,000  pounds. 

f  It  should  also  be  explained  that,  owing  to  the  large  and  very  variable 
amount  of  fine  material  contained  in  the  ore  before  crashing,  as  it  came  from 
the  mine,  it  was  passed  over  the  screen  just  referred  to  before  being  either 
fed  to  the  crusher  or  spalled  by  hand.  Without  this  precaution,  the  results 
of  the  trial  would  have  been  valueless,  as  the  variation  in  the  amount  of  fines 
in  the  original  ore  was  far  greater  than  the  discrepancy  in  the  amount  pro- 
duced by  the  two  different  methods  of  crushing. 


THE    BOASTING  OF   COPPER   OEES  IN  LUMP   FORM.  41 

that,  with  certain  classes  of  ore,  mechanical  crushing  produces 
nearly  double  as  much  fines  as  hand-spaUing.  As  10  per  cent, 
of  fines  is  an  ample  allowance  to  form  a  covering  for  any  kind 
of  roast-heap — and  better  results  are  obtained  when  the  same 
partially  oxidized  material  is  used  over  and  over  again  as  a 
surface  protection — it  may  frequently  occur  that,  in  spite  of  its 
greater  cost,  hand-spalling  may  prove  more  profitable  than 
machine-breaking.  This  is  a  matter  for  individual  decision, 
and  can  be  determined  only  after  a  mature  consideration  of 
the  difference  in  expense  of  the  two  operations,  the  means  at 
hand  for  the  calcination,  and  subsequent  advantageous  smelt- 
ing, of  the  increased  quantity  of  fines,  and  whatever  other 
factors  may  bear  on  the  case  in  hand.  The  following  steps 
should  be  carried  out,  whichever  method  is  decided  upon.  The 
ore,  after  breaking,  should  be  separated  into  three  classes,  the 
largest  including  all  that  product  between  the  maximum  size 
and  one  inch  (25  mm.) ;  the  medium  size,  or  ragging,  consisting 
of  that  class  between  25  mm.  and  the  fine  size  (3  meshes  to 
the  inch,  which  would  give  openings  of  about  6  mm.  net) ;  and 
the  fines,  as  already  explained.  Koughly  speaking,  the  per- 
centage of  each  class,  including  the  fine  ore  that  is  invariably 
produced  during  the  operation  of  mining,  may  be  represented 
by  the  following  figures  : 

Coarse 55  per  cent. 

Ragging 25        " 

Fines , 20 

Total ...100       " 

This  classification  is  effected  with  great  ease  and  economy 
in  case  machine-breaking  is  decided  upon,  by  the  use  of  a 
cylindrical  or  conical  screen  of  -f$  boiler  iron,  about  8  feet  in 
length  and  30  inches  or  more  in  diameter.  This  is  placed 
below  the  breaker  so  that  it  receives  all  the  ore.  It  is  made 
to  revolve  from  18  to  22  times  per  minute,  and  has  a  maxi- 
mum fall  of  an  inch  to  the  foot.  This  can  easily  separate  10 
tons  of  ore  per  hour,  and  by  a  proper  arrangement  of  tracks  or 
bins,  discharge  each  class  into  its  own  bin.  One  fault  in  this 
very  simple  classifying  apparatus  is,  that  the  coarse  lumps  of 
ore  must  necessarily  traverse  all  the  finer  sizes  of  screen,  thus 
greatly  augmenting  the  wear  and  tear.  This  objection,  though 


42        MODEEN  AMEKICAN  METHODS   OF  COPPER  SMELTING. 

frequently  valid  under  other  circumstances,  has  but  little 
weight  when  it  is  remembered  that  even  the  smallest  holea 
(6  mm.)  are  punched  in  iron  of  such  thickness  (A  inch)  that  it 
will  withstand  even  the  roughest  usage  for  many  months.  To 
produce  the  three  sizes  just  alluded  to,  the  screen  requires  two 
sections,  with  holes  respectively  6  mm.  and  25  mm.,  of  which 
the  finer  size  should  occupy  the  upper  5  feet,  and  the  coarser 
the  lower  3  feet  of  the  screen.  In  remote  districts,  where  freight 
is  one  of  the  principal  items  of  expense,  heavy  iron  wire  cloth 
may  be  substituted  for  the  punched  boiler  iron,  and  if  properly 
constructed  and  of  sufficiently  heavy  stock,  will  be  found  satis- 
factory, lasting  about  one  half  as  long  as  the  more  solid  mate- 
rial. The  difference  in  size  between  a  circular  hole  25  mm.  in 
diameter  and  a  square  with  sides  of  that  length,  should  not  be 
overlooked  in  changing  from  one  variety  of  screen  to  the  other. 
The  mouth  of  the  crusher  should  be  level  with  the  feeding- 
floor,  and  the  latter  should  be  covered  with  quarter-inch  boiler 
iron,  firmly  attached  to  the  planks  by  countersunk  screws,  by 
which  arrangement  Jhe  shoveling  is  greatly  facilitated.  With 
such  a  plant,  two  good  laborers  will  feed  the  breaker  at  the  rate 
of  ten  tons  an  hour  for  a  ten-hour  shift,  provided  none  of  the 
rock  is  in  such  masses  as  to  require  sledging,  and  that  the  ore 
is  dumped  close  to  the  mouth  of  the  breaker.  A  seven  by  ten 
jaw-breaker  of  the  best  and  heaviest  make  is  capable  of  crush- 
ing the  amount  just  mentioned  to  a  maximum  size  of  2J  inches, 
provided  the  rock  is  brittle,  heavy,  and  not  inclined  to  clog  the 
machine.  In  most  cases  where  this  duty  is  required,  and 
especially  if  the  ore  is  damp  and  in  large  fragments,  it  is  much 
more  advantageous  to  substitute  a  fifteen  by  nine  breaker, 
which,  when  geared  up  to  230  revolutions  and  with  sufficient 
power,  has  a  capacity  only  limited  by  the  ability  of  the  feeders. 
The  expense  per  ton  of  breaking,  sizing,  and  delivering 
into  cars  with  such  a  plant  operating  upon  ores  of  medium 
tenacity,  is  as  follows,  the  figures  being  deduced  from  average 
results  of  handling  fully  seventy  thousand  tons  under  the  most 
varying  conditions.  It  is  assumed  that  the  breaker  is  run  by 
an  independent  engine  of  sufficient  power,*  while  the  wages  of 

*  Speaking  from  a  very  extensive  experience,  the  author  finds  that  not 
one  breaker  in  ten  is  run  up  to  anything  approaching  its  capacity,  and  that 


THE   ROASTING  OF   COPPER  ORES  IN   LUMP   FORM. 


43 


an  engineer  and  firemen  are  partially  saved  by  taking  the 
steam  from  the  boilers  that  are  supposed  to  supply  the  main 
works : 

COST  OF  BREAKING  ORE  BY   MACHINERY  WITH  A  PLANT  OF    100  TONS 
CAPACITY  IN  TEN  HOURS. 


Power— per  day  of  10  hours  : 
1,200  pounds  of  coal  at  $4.50  per  ton.. $2. 70 

Oil  and  lubricants 40 

Engineer,  \  wages  at  $3 75 

Fireman,  \  wages  at  $2 50 

Labor  : 
Two  feeders  at  $1.75 

Repairs : 

Toggles  and  jaw  plates,  etc $0.43 

Wear  of  tools,  Babbitt  for  renewing 

bearings,  etc 0.37 

Daily  slight  repairs  on  machinery. . . .    0.35 
Miscellaneous  items,  sampling,  etc. . .    0.33 

Sinking  Fund  to  replace  machinery, 
at  10  per  cent,  on  original  cost. . . 


Per  hundred 
tons. 


$4.35 
3.50 


Per  ton 


$0.0435 


0.0350 


1.48 


0.78 


Total $10.11 


0.0148 


0.0078 


$0.1011 


If  it  should  seem  at  first  glance  that  10  cents  per  ton  is  an 
unreasonably  low  figure,  it  will  be  noticed  that  the  cost  of 
transportation  both  to  and  from  the  breaker  is  not  included 
in  this  estimate ;  the  former  is  usually  charged  to  mining  ex- 
penses, and  the  latter  to  heap-roasting.  Ore  that  is  to  undergo 
roasting  in  kilns  for  the  purpose  of  acid  manufacture  must  be 
broken  considerably  smaller  than  that  just  described,  and  this, 
of  course,  lessens  the  capacity  of  the  apparatus  and  propor- 
tionately increases  the  expense.  An  increase  of  50  per  cent, 
in  the  above  estimate  will  be  sufficient  to  cover  it.  The  figures 
given  above  have  been  frequently  attained  by  the  author,  but 
only  under  certain  favorable  conditions,  among  which  are : 
Abundance  of  power  to  run  the  breaker  to  its  full  speed,  re- 
gardless of  forced  feeding.  A  constant  system  of  supervision 

consequently  it  has  become  customary  to  provide  an  engine  and  boiler  far 
too  small  to  drive  the  breaker  up  to  speed  when  doing  full  work.  The  state- 
ments made  above  refer  to  breakers  run  to  their  extreme  capacity,  and  under 
these  conditions  a  7  by  10  crusher  requires  an  engine  of  not  less  than  6  by  10 
cylinder,  while  a  15  by  9  crusher  requires  an  8  by  12  cylinder. 


44       MODERN  AMERICAN   METHODS   OP  COPPER  SMELTING. 

by  which  the  plant  is  kept  up  to  its  full  capacity  of  ten  tons 
per  hour,  and  which  demands  exceptionally  good  men  as  feed- 
ers. A  frequent  inspection  of  the  machinery,  and  renewal  of 
all  jaw  plates,  toggles,  and  other  wearing  parts,  before  the  effi- 
ciency of  the  machine  has  begun  to  be  impaired ;  all  of  which 
repairs  should  be  foreseen  and  executed  during  the  night  shift 
or  on  idle  days.  A  perfect  system  of  checking  the  weight  of 
all  ore  received  and  crushed,  without  which  precaution  a  mys- 
terious and  surprisingly  large  deficit  will  be  found  to  exist  on 
taking  stock.*  It  is  hardly  necessary  to  mention  that  all  bear- 
ings that  cannot  be  reached  while  the  machinery  is  in  motion 
must  be  provided  with  ample  self-oilers,  and  since  clouds  of  dust 
are  generated  in  this  work,  that  unusual'care  must  be  taken  in 
covering  and  protecting  all  boxes  and  parts  subject  to  injury 
from  this  cause.  Unless  the  ore  is  sufficiently  damp— either 
naturally  or  by  artificial  sprinkling — to  prevent  this  excessive 
production  of  dust,  the  feeders  should  be  required  to  wear 
some  efficient  form  of  respirator ;  otherwise,  they  are  likely  to 
receive  serious  and  permanent  injury,  the  fine  particles  of  sul- 
phides being  peculiarly  irritating  to  the  lungs  and  entire  bron- 
chial mucous  membrane. 

The  breaking  of  ore  l>y  hand  hammers,  technically  denomi- 
nated "  spalling,"  is  worthy  of  more  careful  consideration  than 
is  generally  bestowed  upon  it.  The  style  of  hammer  is  seldom 
suited  to  the  purpose,  though  both  the  amount  of  labor  accom- 
plished and  the  personal  comfort  of  the  workmen  depend  more 
upon  the  weight  and  shape  of  this  implement  and  its  handle 
than  on  any  other  single  factor  save  the  quality  of  the  ore  it- 
self. There  should  be  several  cast- steel  sledges,  differing  in 
weight  from  6  to  14  pounds,  and  intended  for  general  use 
in  breaking  up  the  larger  fragments  of  rock  to  a  size  suit- 
able for  the  light  spalling-hammers.  Each  laborer  should  be 


*  This  is  a  difficulty  that  the  metallurgist  will  encounter  at  every  stage 
of  his  work.  In  spite  of  the  most  accurate  scales,  and  of  careful  and  frequent 
determinations  of  weights,  the  quarterly  balance-sheet  will  invariably  show 
that  the  actual  amount  of  ore  treated  is  less  than  the  amount  shown  by  the 
weigh-master's  book;  while  the  weights  of  all  supplies  consumed,  especially 
fuel,  have  been  reported  .too  low.  To  one  unprepared  for  this  result,  the 
consequences  may  be  serious. 


THE   BOASTING  OF   COPPER   ORES   IN  LUMP   FORM.  45 

provided  with  a  hammer  6  inches  in  length,  forged  from  a 
1J  inch  octagonal  bar  of  the  best  steel,  and  weighing  about 
2|  pounds.  This  should  be  somewhat  flattened  and  ex- 
panded at  the  middle  third,  to  give  ample  room  for  a  handle 
of  sufficient  size  to  prevent  frequent  breakage.  The  handles 
usually  sold  for  this  purpose  are  a  constant  source  of  annoy- 
ance and  expense,  being"  totally  unsuited  to  this  peculiar 
duty.  It  is  better  to  have  the  handles  made  at  the  works,  if 
it  is  possible  to  procure  the  proper  variety  of  oak,  ash,  hick- 
ory, or,  far  better  than  all,  a  small  tree  known  in  New  England 
as  iron-wood  or  hornbeam,  which,  when  peeled  and  used  in  its 
green  state,  excels  any  other  wood  for  toughness  and  elasticity. 
The  handles  should  -be  perfectly  straight,  without  crook  or 
twist,  so  that,  when  firmly  fastened  in  the  eye  of  the  hammer 
by  an  iron  wedge,  the  hammer  hangs  exactly  true.  Their 
value  and  durability  depend  much  upon  the  skill  with  which 
the  handles  are  shaved  down  to  an  area  less  than  half  their 
maximum  size,  beginning  at  a  point  some  6  inches  above  the 
hammer-head  and  extending  for  about  ten  inches  toward  the 
free  extremity.  If  properly  made  and  of  good  material,  they 
may  be  made  so  small  as  to  appear  liable  to  break  at  the  first 
blow ;  but  in  reality  they  are  so  elastic  that  they  act  as  a 
spring,  and  obviate  all  disagreeable  effects  of  shock;  wear 
longer  and  do  more  work  than  the  ordinary  handle.  Such  a 
handle  has  lasted  five  months  of  constant  use,  in  the  hands  of 
a  careful  workman,  whereas  one  of  the  ordinary  make  has  an 
average  life  of  scarcely  four  days,  or  perhaps  thirty  tons  of  ore. 
Where  the  ore  is  of  pretty  uniform  character,  it  is  advanta- 
geous to  adopt  the  contract  system  for  this  kind  of  work.  A 
skillful  laborer,  under  ordinary  conditions,  will  break  seven 
tons  of  rock  per  ten  hour  shift  to  a  size  of  2J  inches,*  taking 
coarse  and  fine  as  it  comes,  and  in  some  cases  he  is  also  able 
to  assist  in  screening  and  loading  the  same  into  cars.  This 
latter  operation  should  be  executed  with  an  ordinary  strong 
dung-fork  having  such  spaces  between  the  tines  as  to  retain 
the  coarsest  size,  while  the  finer  classes  are  left  upon  the 

*  Unless  otherwise  specified,  the  term  "day"  or  "shift"  may  be  under- 
stood to  signify  the  ordinary  working  day  of  ten  hours,  from  seven  A.M.  to 
six  P.M.,  with  one  hour  for  dinner. 


46        MODERN  AMERICAN   METHODS   OF   COPPER  SMELTING. 

ground.  When  a  sufficient  quantity  of  the  latter  has  accu- 
mulated and  the  pile  or  stall  is  ready  to  receive  its  outer  layer 
of  ragging,  the  mixed  material  should  be  thrown  upon  a  screen 
inclined  to  an  angle  of  about  48  degrees  and  having  three 
meshes  to  the  inch.  This  screen  is  elevated  upon  legs  to  such 
a  height  that  the  coarser  class  that  fails  to  pass  its  openings 
will  be  caught  in  a  car  or  barrow,  while  the  fines  fall  either 
into  a  second  movable  receptacle  or  upon  the  floor,  being  in 
the  latter  case  prevented  from  again  mixing  with  the  un- 
screened ore  by  a  tight  boarding  on  the  front  and  sides  of  the 
screen  frame.  The  amount  of  space  required  for  convenient 
spalling  is  about  forty  square  feet  per  man,  which  will  aUow 
for  ore-dumps,  tracks,  sample  boxes,  etc.  A  good  light  is 
essential,  especiaUy  if  any  sorting  is  to  be  done,  and  it  is  in 
this  case  and  where  fuel  is  expensive  that  hand  spalling  fre- 
quently presents  especial  advantages.  When  the  ores  are 
siliceous,  a  mere  rejection  of  such  pieces  of  barren  quartz  or 
wall  rock  as  have  accidentally  got  among  the  ore,  or  first 
become  visible  on  breaking  up  the  larger  masses,  may  have  a 
most  beneficent  influence  on  the  subsequent  fusion.  Where 
the  expense  of  treatment  is  high  and  work  is  conducted  on  a 
large  scale,  the  profit  resulting  from  raising  the  average  con- 
tents of  the  ore  even  a  single  per  cent,  is  hardly  credible,  even 
aside  from  the  increased  fusibility  due  to  the  diminished  pro- 
portion of  silica.  To  illustrate :  At  certain  works  that  the 
author  was  called  to  superintend,  it  had  been  the  custom  to 
spall  all  the  first-class  ore  just  as  it  came  from  the  mine  with- 
out any  sorting  out  of  barren  wall  rock,  considerable  quantities 
of  which  were  mixed  with  the  ore.  Fuel  and  labor  were  very 
high,  and  the  ore  mixture  already  too  siliceous.  A  rough 
method  of  sorting  was  instituted,  and  some  twelve  per  cent, 
of  the  entire  weight  of  the  first-class  ore  was  thrown  out  with 
the  loss  of  scarcely  any  metal.  The  month's  average  assay  of 
ore  due  solely  to  this  sorting  was  increased  2J  per  cent.,  and 
the  furnaces  gave  an  extra  yield  of  1,500  pounds  of  copper 
from  30  tons  daily,  or  45,000  pounds  for  the  month,  which,  cal- 
culated on  the  spot  at  10  cents  per  pound,  was  a  gain  of  $4,500. 
The  net  gain  was  probably  even  more  than  this ;  for  the  ex- 
pense of  sorting  was  hardly  appreciable,  while  the  increased 


THE   ROASTING  OF   COFFEE  ORES  IN   LUMP  FORM.  47 

fusibility  of  the  charges,  and  the  fact  that  3,000  pounds  of  bar- 
ren material  could  be  replaced  by  an  equal  amount  of  good 
ore,  added  largely  to  the  profits. 

All  windows  in  the  spalling-shed  must  be  protected  by 
strung  iron  wire  netting,  three  meshes  to  the  inch ;  nor  should 
the  eyes  of  the  workmen  receive  less  care  than  the  panes  of 
glass.  Accidents  from  flying  fragments  of  sharp  rock  are  com- 
mon, and  frequently  result  in  a  partial  or  total  loss  of  vision, 
which  entails  serious  expense  on  the  company,  and  is  an  inflic- 
tion almost  worse  than  death  upon  the  victim.  All  this  can 
be  easily  avoided  by  the  use  of  wire  goggles,  strongly  and 
properly  made,  so  that  while  completely  protecting  the  visual 
organs,  they  cause  but  little  annoyance  to  the  wearer.  These 
should  be  furnished  by  the  employer,  and  should  be  constantly 
worn  on  pain  of  dismissal.  The  workman,  with  proverbial 
recklessness,  will  sometimes  claim  that  he  has  a  right  to  risk 
his  own  eyes  if  he  chooses  ;  but  the  employer  may  demand  the 
privilege  of  protecting  himself  against  tiiose  claims  which,  with 
more  or  less  reason,  are  sure  to  be  made  in  case  of  injuries 
received  while  in  his  employ.  Artificial  warming  of  the  build- 
ing is  neither  necessary  nor  desirable,  the  work  being  of  such 
a  nature  as  to  obviate  suffering  from  cold,  provided  the  feet 
are  properly  protected.  Lithe,  active  men  or  boys,  of  nervous 
temperament  and  quick,  accurate  movements,  should  be  se- 
lected for  this  work,  which  calls  rather  for  rapidity  and  knack 
than  for  any  great  muscular  effort.  The  amount  of  rock  broken 
being  about  proportionate  to  the  number  of  effective  blows 
delivered,  it  follows  that,  other  things  being  equal,  a  man  who 
delivers  twenty  blows  per  minute  will  accomplish  nearly  dou- 
ble the  work  of  one  whose  deliberate  temperament  would  nat- 
urally limit  his  motions  to  half  that  number  during  the  same 
time.  It  is  just  in  this  matter  of  selecting  workmen  adapted 
to  each  variety  of  labor  that  long  experience  in  the  manage- 
ment of  men,  and  a  thorough  knowledge  of  human  nature, 
enable  one  man  to  obtain  results  and  effect  improvements  that 
seem  well-nigh  impossible  to  him  who  is  unaccustomed  to  such 
a  perfect  adaptation  of  means  to  ends. 

The  cost  of  spalling  an  ore  of  the  same  character  as  that 
on  which  the  foregoing  estimates  for  machine-breaking  are 


48        MODEKN   AMEKICAN  METHODS   OF   COPPER   SMELTING. 

based  has  been  calculated  from  the  average  results  of  a  very 
large  quantity  of  ore,  assuming  100  tons  to  be  spalled, 
screened,  and  loaded  in  ten  hours. 

COST  OF  SPALLING  ORE  BY  HAND  WITH    AN    OUTPUT  OF    100  TONS  PER  10 

HOURS. 

Labor  :  Per  100  tons.     Per  ton. 
14  men  breaking  ore,  including  screen- 
ing and  loading,  at  $1.50 $21.00 

4  men  sledging  and  loading  at  $1.50. .       6.00 

1  foreman 2.50          $'29.50        $0.295 

Repairs : 

Including  new  steel  and  handles. 

5  handles  at  30  c 1.50 

7  pounds  of  steel  at  15  c 1 .05 

Blacksmith's  and  other  work  on  above, 

i  day 1.00 

Screens,  forks,  and  shovels 1.67 

General  repairs 0.55  5.77       0.0577 

Sinking  fund : 

To    replace    screens    and    permanent 
fixtures..  0.15         0.015 


Total $35.42    $0.3542 

This  is  about  25  cents  per  ton  greater  than  by  machine- 
breakiag.  The  same  addition — 50  per  cent. — will  here  also 
cover  the  increased  cost  of  breaking  the  ore  smaller  for  kiln 
roastiog. 

I.   HEAP  BOASTING. 

The  roasting  of  sulphureted  ores  or  copper  in  mounds  or 
heaps  dates  back  beyond  the  age  of  history,  and  in  its  most 
primitive  form  is  still  practiced  among  barbarous  nations  who 
have  evidently  never  held  communication  with  each  other. 
It  is  not  difficult  to  imagine  its  origin  in  the  midst  of  some 
rude  people,  whose  possession  of  superficial  deposits  of  oxides 
and  carbonates  of  copper  had  taught  them  the  value  of  that 
metal  as  obtained  by  a  simple  process  of  fusion,  while  the  sul- 
phide ores  that  were  doubtless  encountered  at  a  slightly 
greater  depth  were  thrown  aside  in  heaps  as  worthless  until 
the  spontaneous  combustion  of  some  of  these  waste-piles, 
brought  about  by  the  decomposition  of  the  sulphides,  and  the 
interesting  discovery  that  ores,  hitherto  considered  valueless, 


THE  BOASTING  OF   COPPER   ORES   IN  LUMP   FORM.  49 

would,  after  a  simple  burning,  also  yield  the  coveted  metal, 
led  some  metallurgist  of  that  day  to  the  idea  of  calling  in  the 
aid  of  artificial  combustion  to  hasten  matters.  Nor  has  this 
rude  and  simple  process  undergone  that  general  improvement 
that  one  might  have  expected  when  considering  the  tremen- 
dous advances  made  in  other  appliances  for  accomplishing  the 
same  purpose.  A  somewhat  careful  inspection  of  nearly  all 
the  localities  in  the  United  States  where  heap  roasting  is  prac- 
ticed reveals  the  fact  that  the  results  obtained  are  far  from 
satisfactory  in  the  greater  number  of  instances.  The  amount 
of  fuel  employed  and  the  height  and  size  of  the  heap  are  not 
correctly  proportioned  to  the  sulphur  contents  of  the  particular 
ore  under  treatment.  Fragments  of  rock  far  exceeding  in  size 
the  extreme  proper  limit,  as  determined  by  experience,  are 
mixed  with  material  so  fine  as  to  be  fitted  only  for  the  covering- 
layer,  and  these  are  dumped  upon  the  ill-arranged  bed  of  fuel 
without  regard  to  the  final  shape  of  the  structure  or  the  estab- 
lishment and  maintenance  of  the  requisite  draught.  Also,  a 
sufficient  quantity  of  proper  material  for  the  all-important  cov- 
ering-layer is  not  applied.  The  result  of  these  and  some  other 
deficiencies  is  that  a  small  proportion  only  of  the  ore  is  exposed 
to  a  proper  degree  of  heat,  and  the  remainder  of  the  heap  is 
pretty  equally  made  up  of  half-molten  masses  of  clinkers  from 
the  interior,  and  comparatively  raw  and  unburned  material 
from  the  outer  layer.  With  the  exception  of  what  little  sul- 
phur may  have  been  driven  off  by  volatilization,  the  ore  after 
such  a  calcination  is  scarcely  better  fitted  for  the  fusion  that  is 
to  follow  than  if  it  had  not  been  roasted.  The  evil  results  of 
an  imperfect  preliminary  calcination  can  only  be  fully  appre- 
ciated after  the  ore  has  passed  to  the  next  stage  of  treatment ; 
in  fact,  they  are  so  far-reaching  that  it  is  impossible  to  express 
the  full  measure  of  the  damage  in  exact  figures.  A  discussion 
of  the  effect  of  imperfect  calcination  and  of  its  remedies  will  be 
found  under  the  head  of  u  Smelting  Sulphide  Ores  in  Blast- 
Furnaces."  The  vital  importance  of  the  process,  and  the 
almost  universal  want  of  care  and  supervision  in  the  carrying 
out  of  its  details,  will  justify  this  urgent  remonstrance  against 
its  improper  execution.  Moreover,  the  cost  of  roasting  prop- 
erly is  no  greater  than  that  of  doing  it  imperfectly. 
4 


50        MODEKN  AMEEICAN  METHODS   OF   COPPER  SMELTING. 

The  responsibility  of  selecting  heap  roasting  in  contradis- 
tinction to  the  other  methods  enumerated  for  the  desulphuriza- 
tion  of  an  ore  must  rest  upon  the  metallurgist  in  charge  of  the 
works,  and  is  a  question  deserving  the  most  careful  considera- 
tion ;  nor  are  the  reasons  for  or  against  its  adoption  in  most 
cases  so  clear  and  self-evident  that  plain  and  unvarying  rules 
can  be  laid  down  for  his  guidance.  In  this,  as  in  many  other 
instances,  there  are  usually  strong  metallurgical,  commercial, 
and  sanitary  arguments  that  should  be  carefully  weighed.  The 
contiguity  of  cultivated  land,  or  even  of  valuable  forests,  would 
forbid  the  employment  of  heap  roasting  unless  the  arguments 
for  its  adoption  were  sufficiently  powerful  to  outweigh  the  an- 
noyance of  constant  remonstrances  on  the  part  of  the  land- 
owners, accompanied  by  claims  for  heavy  damages  from  the 
effect  of  the  sulphurous  gases.  For  legal  reasons,  as  well  as 
for  various  other  prudential  and  sanitary  motives,  it  is  impor- 
tant to  learn  how  this  damage  is  effected,  and  to  what  distance 
its  ravages  may  extend. 

1.  The  damage  is  caused  solely  by  sulphurous  and  sulphuric 
acids,  neither  arsenical  nor  antimonial  fumes  nor  the  thick 
clouds  of  smoke  evolved  from  bituminous  coal  having  any  ap- 
preciable influence. 

2.  The  most  injurious  effects  are  visible  on  young,  growing 
plants;  and  the  more  tender  and  succulent  their  nature,  the 
more  rapid  and  fatal  are  these. 

3.  A  moist  condition  of  the  atmosphere  greatly  heightens 
the  injurious  effects  of  the  gases,  and  as  our  most  frequent 
rains  occur  in  the  spring,  at  the  very  period  during  which  the 
crops  and  forests  are  in  young,  green  leaf,  more  damage  may 
be  effected  in  a  few  days  at  this  season  than  during  the  entire 
remainder  of  the  year.     The  author  has  seen  a  passing  cloud, 
while  floating  over  a  dozen  active  roast  piles,  absorb  the  sul- 
phurous smoke  as  rapidly  as  it  arose,  and,  after  being  wafted 
to  a  distance  of  some  eight  miles  by  a  gentle  breeze,  fall  in  the 
shape  of  an  acrid  and  blighting  rain  upon  a  field  of  young 
Indian  corn,  withering  and  curling  up  every  green  leaf  in  the 
whole  tract  of  many  acres  in  less  than  an  hour. 

4.  As  might  be  expected,  the  vegetation  nearest  the  spot 
where  the  fumes  are  generated  suffers  the  most,  and  the  direc- 


THE   ROASTING   OF   COPPER   ORES   IN   LUMP   FORM.  51 

tion  of  the  prevailing  winds,  in  a  fertile  district,  can  be  plainly 
determined  by  the  sterile  appearance  of  the  tract  over  which 
they  blow. 

The  most  elaborate  means  for  obviating  this  evil  have  been 
tried  at  the  great  metallurgical  establishments  of  Europe,  and 
vast  sums  have  been  expended  in  this  direction.  The  plans 
pursued  in  England  tend  more  toward  the  mechanical  deposi- 
tion of  the  offending  substances  in  long  flues  and  passages  (the 
first  experimenters  evidently  having  failed  to  realize  that  the 
sulphurous  vapors  alone  caused  the  damage),  while  in  Germany, 
the  more  scientifically  correct  method  of  effecting  condensation 
and  absorption  of  the  gases  by  means  of  various  liquids  and 
chemicals  was  pursued,  but  with  scarcely  better  results.  In 
the  former  case,  it  was  soon  discovered  that,  while  the  oxides 
of  zinc,  lead,  arsenic,  antimony,  and  various  other  substances 
carried  over  mechanically  or  as  gases  by  the  draught,  were 
condensed  and  deposited  so  completely  in  the  canals  that  the 
air  issuing  from  the  top  of  the  tall  chimney  was  practically  free 
from  them,  the  percentage  of  sulphurous  and  sulphuric  acids, 
which  alone  are  reponsible  for  damage  to  vegetation,  was  not 
sensibly  diminished.  Similar  efforts  in  Germany  for  the 
absorption  of  the  sulphur  gases  were  carried  out  with  such 
imperfect  and  ill-adapted  apparatus,  and  on  so  inadequate 
a  scale,  that  the  absolute  impossibility  of  a  successful  issue 
must  be  apparent  to  any  one  reading  the  pamphlet  issued  by 
the  Freiberg  officials  intrusted  by  government  with  the  execu- 
tion of  the  experiments.  But  however  insufficient  the  appar- 
atus, the  results  arrived  at  decisively  indicated  the  impossibility 
of  disposing  of  the  offending  fumes  by  any  plan  of  condensation 
or  chemical  absorption,  except  on  a  small  scale  and  with  unusu- 
ally dilute  gases. 

The  problem  has  long  been  solved  in  Europe  in  the  only 
rational  and  economical  manner,  by  utilizing  the  hitherto 
destructive  fumes  for  the  manufacture  of  sulphuric  acid.  This 
requires,  of  course,  the  abolition  of  heap  roasting,  and  the  con- 
finement of  all  processes  of  calcination  to  such  closed  kilns  and 
furnaces  as  may  be  placed  in  direct  communication  with  the 
leaden  acid  chambers.  The  very  secondary  position  held  by 
agriculture  in  those  sections  of  our  country  that  furnish  the 


52        MODERN  AMEEICAN   METHODS   OF   COPPER  SMELTING. 

material  for  the  principal  smelting- works  lias,  up  to  the  present 
time,  obviated  any  necessity  of  dealing  with  this  question, 
though  some  of  the  largest  copper  smelting-works  in  the  East  * 
have  already  adopted  the  European  solution  of  the  problem  as 
a  matter  of  profit  rather  than  necessity. 

In  the  case  of  smelting  establishments  of  such  capacity  that 
not  more  than  twenty-five  tons  daily  of  sulphur  are  oxidized 
and  poured  into  the  atmosphere,  it  is  probable  that  all  vegeta- 
tion outside  of  a  circle  of  four  miles  in  diameter  may,  under 
ordinary  circumstances,  be  considered  safe  from  the  effects  of 
the  fumes. 

No  harm  to  man  or  beast  has  ever  been  authentically  reported 
as  resulting  from  the  use  as  an  article  of  food  of  vegetable  origin 
that  has  been  exposed  to  the  corrosive  influence  of  such  gases. 
This  is  a  very  important  point^  and  careful  investigation  and 
experiments  have  completely  disproved  the  opposing  argu- 
ments so  often  made  against  smelting-works  in  Germany  by 
certain  stock-raisers. 

In  laying  out  the  ground  for  roast-piles,  the  first  point  to 
consider  is,  the  prevailing  direction  of  the  wind,  great  care  be- 
ing taken  that  the  fumes  shall  neither  be  blown  toward  the 
works  themselves,  nor  toward  the  offices  and  dwelling-houses 
in  their  immediate  neighborhood.  Smelting-works  are  fre- 
quently situated  in  a  valley,  in  which  the  prevailing  winds 
naturally  follow  its  longitudinal  axis.  In  this  case,  a  tract  of 
ground  on  one  side  or  other  of  the  central  depression,  instead 
of  in  its  immediate  course,  should  be  selected.  By  careful  ob- 
servation, and  taking  into  consideration  that  the  prevailing 
winds  may  differ  at  different  seasons  of  the  year,  the  roast 
heaps  can  generally  be  so  placed  as  to  give  no  substantial 
ground  for  claims  of  damage  to  agriculture.  Care  should  also 
be  taken  that  the  selected  tract  is  free  from  any  possible 
chance  of  inundation ;  that  it  is  either  perfectly  dry,  or  sus- 
ceptible of  thorough  drainage  ;  that  it  is  not  crossed  by  gullies 
or  depressions  that  may  serve  as  water-courses  for  the  drain- 
age of  the  surrounding  hills  in  case  of  a  heavy  shower ;  that 
it  is  protected  as  far  as  possible  from  violent  winds;  that 

*  The  Orford  Copper  and  Sulphur  Company,  of  New  Jersey,  and  G.  H. 
Nichols  &  Co.,  of  New  York. 


THE  ROASTING  OF   COPPER   ORES   IN   LUMP   FORM.  53 

snow  does  not  drift  on  it  badly  in  winter,  and  that  it  is  at 
least  as  high  as  the  spot  to  which  the  ore  is  to  be  transported 
for  the  ensuing  operation,  or,  if  this  is  not  feasible,  at  least  as 
high  as  the  elevator  which  is  to  raise  it  to  the  required  level. 
If  possible,  it  should  occupy  an  intermediate  position,  as  re- 
gards grade,  between  the  shed  in  which  the  ore  is  prepared 
for  roasting,  and  the  point  at  which  the  calcined  product  is  to 
be  delivered.  A  fall  of  ten  feet  for  the  first  step  and  four  and 
one  half  or  more  for  the  second — total  fourteen  and  one-half 
feet — will  render  possible  the  establishment  of  a  system  of 
handling  and  transportation  that  can  hardly  be  exceUed. 

A  detailed  description  of  such  a  model  plant  will  suffice  as 
a  pattern  that  may  be  varied  to  suit  local  conditions,  always 
remembering  that,  under  ordinary  American  circumstances, 
the  economy  of  labor  is  one  of  the  first  conditions  to  be  ob- 
served, and  that  the  saving  of  25  cents  in  handling  a  ton  of 
crude  ore  is  equal  to  a  dollar  or  more  on  the  ton  of  matte,  and 
at  least  two  dollars  when  estimated  on  the  ton  of  copper. 

Assuming  that  the  metallurgist  is  called  upon  to  prepare  a 
yard  for  heap  roasting  of  ample  size  to  contain  a  sufficient 
number  of  piles  to  furnish  from  80  to  100  tons  daily  of  cal- 
cined material,  without  encroaching  upon  the  partially  burned 
ore,  and  that  the  contour  of  the  ground  permits  the  requisite 
fall  in  each  direction — as  already  explained — the  following 
plan  may  be  advantageously  adopted  : 

Experience  having  demonstrated  that  an  ordinary  pile  40 
feet  long,  24  feet  wide,  and  6  feet  high  will  contain  about  240 
tons,  and  burn  for  70  days,  to  which  should  be  added  10  days 
for  removing  and  rebuilding,  it  follows  that  each  pile  will  sup- 
ply zffl  =  3  tons  of  roasted  ore  daily ;  so  that  35  heaps  will  be 
needed  to  furnish  the  full  amount  of  100  tons  daily.  Allow- 
ing 36  feet  for  the  width  of  each  structure,  and  60  feet  for  the 
length,  in  order  to  give  ample  room  for  various  purposes  that 
will  be  explained  hereafter,  an  area  of  75,600  square  feet  will 
be  required. 

The  frost  being  out  of  the  ground  and  the  surface  dry,  a 
rectangular  area  of  the  extent  just  computed  should.be  pre- 
pared by  means  of  plow  and  scraper,  being  leveled  to  a  perfect 
plane,  and  having  a  slight  slope  toward  one  longitudinal  edge, 


54       MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

or  from  a  central  ridge  toward  either  side.  The  black  surface 
soil  should  be  removed,  together  with  all  sods,  stumps,  and 
remains  of  vegetation,  and  the  space  that  it  occupied  replaced 
with  broken  stones,  slag,  or  coarse  tailings  from  the  concen- 
trator ;  or,  best  and  cheapest  of  all,  granulated  slag  from  the 
blast-furnace.  This  can  be  easily  obtained  in  any  desired 
amount  by  allowing  the  molten  scoria  from  the  slag-spout  to 
drop  into  a  wooden  trough,  lined  with  sheet  iron,  placed  with 
a  grade  of  one  inch  to  the  foot,  and  provided  with  a  stream  of 
water  running  through  it,  equal  to  at  least  sixty  gallons  a 
minute.  If  sufficient  fall  is  available,  the  granulated  slag — 
graduated  to  any  desired  size  by  the  height  through  which  it 
falls,  velocity  and  amount  of  water,  and  various  other  trifling 
factors  easily  ascertained  by  trial — is  discharged  directly  from 
the  launder  into  dump-carts,  the  water  being  drawn  off  by  sub- 
stituting a  sieve  of  ten  meshes  to  the  linear  inch  for  the  lower 
eighteen  inches  of  the  wooden  trough  bottom.  By  this  sim- 
ple means,  the  best  kind  of  filling  can  be  prepared  and  deliv- 
ered at  the  roasting-yard  for  nothing,  the  expense  of  transpor- 
tation hardly  equaling  the  wages  of  the  ordinary  slag-men, 
who  may  be  employed  in  attending  to  the  loading  of  the  carts 
and  the  leveling  of  the  material  when  dumped.  The  entire 
area  of  the  rectangle  being  raised  at  least  two  inches  above 
the  surrounding  ground,  a  proper  surface  is  formed  by  spread- 
ing upon  the  foundation  already  described  a  sufficient  quan- 
tity of  clayey  loam.  This  should  be  rolled  several  times  with 
a  heavy  roller  drawn  by  horses,  the  surface  being  slightly 
dampened  from  time  to  time,  until  the  entire  area  is  as  level  and 
nearly  as  hard  as  a  macadamized  road.  Assuming  a  fall  of 
some  10  feet  between  the  spalling-shed  and  the  ground  under 
consideration,  an  elevated  track  is  constructed  over  the  central 
longitudinal  axis  of  this  rectangle,  for  the  purpose  of  delivering 
the  broken  ore  upon  the  heaps.  Where  no  side-hill  is  avail- 
able, the  ore  is  carried  up  on  to  the  heaps  in  wheelbarrows. 
The  trestles  to  support  the  track  may  consist  of  sets  or  bents 
of  two  8-inch  by  12-inch  posts  with  8-inch  by  10-inch  caps  6 
feet  long.  Bents  36  feet  apart  and  properly  braced.  The 
posts  should  be  about  6  feet  apart  at  the  bottom  and  2  or  3 
feet  apart  at  the  top. 


THE  BOASTING  OF   COPPER  ORES   IN  LUMP   FORM. 


55 


These  bents  support  the  trussed  beams,  10  inches  by  12 
inches,  on  edge,  which  carry  the  track  as  shown  in  the  accom- 


panying sketch.     These  girders  may  be  made  up  of  2-inch  or 
3-inch  plank  spiked  together. 


56        MODERN   AMERICAN   METHODS   OF  COPPER  SMELTING. 

A  fall  of  an  inch  in  12  feet  will  greatly  facilitate  the  hand- 
ling of  the  loaded  car,  and  offer  little  obstruction  to  the  return 
of  the  empty  one.  The  track  should,  if  possible,  consist  of 
T-rails,  12  pounds  to  the  yard,  firmly  spiked  to  the  longitudi- 
nal stringers,  no  sleepers  being  necessary  ;  and  well-connected 
with  each  other  by  fish-plates,  having  two  half-inch  bolts  at 
each  end  of  each  rail.  All  tracks  throughout  the  entire  estab- 
lishment should  have  the  same  gauge  ;  22  inches  is  a  conven- 
ient standard. 

An  iron-bodied  end-dumping  car,  so  made  as  to  dump  at 
right  angles  to  the  track,  should  be  used.  As  the  heaps  are 
some  40  feet  in  length,  the  area  over  which  the  ore  can  be 
distributed  by  dumping  from  the  car  is  far  too  contracted,  and 
the  following  simple  contrivance  will  be  found  to  save  many 
thousand  dollars  annually  that  would  otherwise  be  expended 
in  spreading  the  ore  by  hand :  a  plate  of  f-inch  boiler  iron, 
30  inches  square,  fitted  with  a  pair  of  short,  low  rails,  on 
three  sides  of  it,  is  so  cut  and  placed  upon  the  stationary  track 
that  the  loaded  car,  striking  first  the  flattened  extremities  of 
one  set  of  the  short  rail  pieces,  while  the  flanges  of  the  wheels 
run  in  corresponding  slits  until  elevated  upon  the  turn-table 
by  the  gradual  increasing  height  of  the  short  rails  referred  to, 
the  heavy  car  may  be  easily  turned  upon  the  greased  plate  by 
a  single  workman,  being  held  and  guided  to  the  similar  pair  of 
short  rails  placed  at  right  angles  to  those  already  described  by 
a  circular  guard  rail,  fastened  at  that  end  of  the  plate  opposite 
to  the  point  of  entrance.  A  temporary  track,  formed  of  a  pair 
of  heavy  rails,  held  firmly  together,  prevented  from  spreading 
by  cross-ties,  and  supported  by  movable  trestles,  is  laid  at  right 
angles  to  the  main  railroad,  corresponding  exactly  to  a  pair  of 
the  short  side  rails  on  the  turn-table  plate.  It  will  be  readily 
seen  that,  by  this  simple  contrivance,  the  extreme  end  of  the 
longest  roast-pile  can  be  reached  with  the  loaded  car,  while 
the  turn-table  plate  can  be  shifted  backward  and  forward  until 
every  square  foot  of  the  heap  has  received  its  proper  quota  of 
ore.  The  accompanying  dimensioned  drawing  illustrates  suffi- 
ciently the  principal  arrangements  described  in  the  preceding 
pages.  If  the  contour  of  the  surface  permit,  one  longitudinal 
side  of  the  prepared  yard  should  be  bounded  by  a  wall  about 


THE  BOASTING   OF   COPPER   ORES   IN   LUMP   FORM.  57 

four  feet  in  height,  the  top  of  the  same  being  level  with  the 
ground  on  which  the  roast-heaps  are  built,  while  a  railroad 
leading  to  the  furnaces  is  constructed  parallel  with  it,  in  such 
a  manner  that  the  calcined  ore  may  be  wheeled  on  a  plank  and 
dumped  directly  into  cars  without  having  to  ascend  any  grade, 
thus  greatly  lessening  the  expense  of  loading.  The  labor  and 
cost  of  preparing  a  plant,  such  as  has  been  just  described,  will 
be  quickly  repaid  by  the  consequent  avoidance  of  the  waste 
inseparable  from  a  moist  and  muddy  roasting  yard,  and  espe- 
cially from  water  flowing  between  the  heaps.  A  case  came 
under  the  author's  observation,  where  the  want  of  proper  facil- 
ities for  carrying  off  surface  water  has  caused  a  loss  estimated 
at  $12,000  within  an  hour,  merely  from  the  material  washed 
away  by  the  back-water  from  a  swollen  ditch,  which  passed 
between  the  roast-heaps,  but  which,  from  motives  of  economy, 
had  been  made  too  small  to  carry  off  unusual  floods. 

The  height  of  the  pile  must  depend  entirely  upon  the  char- 
acter of  the  ore  and  the  time  for  calcination  at  the  disposal  of 
the  metallurgist.  The  higher  the  heap,  the  more  fiercely  it  will 
heat,  and  the  longer  it  will  take  to  complete  the  operation. 
Consequently,  where  the  ore  is  rich  in  sulphur,  and  when  time 
is  an  object,  as  where  the  supply  for  the  furnaces  is  small,  heaps 
should  be  made  low. 

An  ore  with  12  per  cent,  sulphur,  which  is,  perhaps,  as  low 
as  can  be  thoroughly  roasted  in  heaps  without  the  intermixing 
of  a  considerable  quantity  of  fuel  throughout  with  the  rock 
may  be  piled  up  to  a  height  of  7  feet  advantageously,  while  solid 
pyrites  with  a  sulphur  tenor  of  from  35  to  40  per  cent,  should 
never  be  allowed  to  exceed  5  or  5^  feet,  the  measurement  in- 
cluding only  the  ore,  and  not  the  layer  of  wood  on  which  it 
rests.  The  best  average  height  for  ordinary  ore  is  6  feet,  under 
which  circumstances  it  will  burn  70  days ;  the  time  being  cor- 
respondingly diminished  or  increased  by  10  days,  if  6  inches 
be  taken  from,  or  added  to,  the  above  figures.  The  area  of  the 
heap  has  little  influence  on  this  time.  The  following  table 
gives  the  result  of  the  roasting  of  large  quantities  of  various 
ores.  In  most  of  these  cases,  frequent  sulphur  assays  were 
made  of  the  ore  under  treatment ;  but  in  a  few  instances,  the 
sulphur  was  estimated  from  a  general  knowledge  of  the  mate- 


58        MODEEN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

rial.  The  heaps  were  thoroughly  covered  and  carefully 
watched,  and  the  combustion  was  kept  at  the  lowest  point 
compatible  with  safety,  the  sole  object  being  to  obtain  the  most 
thorough  possible  roast  regardless  of  time  or  trouble. 

This  should  be  the  universal  practice ;  for  although  the 
grade  of  metal  to  be  produced  in  the  subsequent  fusion  may 
not  demand  such  a  thorough  calcination,  it  is  better  to  roast  a 
certain  portion  of  the  stock  thoroughly,  and  then  reduce,  or 
dilute,  the  matte  to  the  required  standard  by  the  addition  of 
raw  ore.  This  lessens  expenses  in  various  ways.  It  costs  but 
little  more  to  roast  an  ore  thoroughly  than  to  do  so  partially ; 
and  the  more  completely  the  sulphur  is  eliminated  from  the 
roasted  ore,  the  larger  will  be  the  proportion  of  raw  ore  that 
can  be  used  in  the  charge  ;  and  consequently,  the  less  will  be 
the  cost  of  calcining  and  the  losses  from  fines  of  roasted  ore. 
It  is  also  very  easy  to  keep  the  "  pitch  "  or  percentage  of  the 
matte  produced  at  a  proper  point,  when  thoroughly  oxidized 
stock  is  always  at  hand.  These,  and  various  other  reasons 
that  could  be  mentioned,  are  sufficient  to  refute  the  arguments 
of  those  who  consider  the  addition  of  raw  ore  peculiarly  inju- 
rious, and  prefer  an  imperfect  roasting  of  the  entire  stock. 

LENGTH  OF  TIME  CONSUMED  IN  BURNING  HEAPS  OF  VARIOUS  HEIGHTS. 

Height  QnaWv  of  nrp  Per  cent-        Per  cent-  Days  No.  of 

infect.  Quality  o.  sulphur.         copper.          burning.  sample. 

5  ....Pjrite 39  6|  54  No,     1 

5 Chalcopyrite,  with  little  py- 

rite  in  quartz 18  14 -3  41 

5 Bornite  and  pyrite 31  21*4  53 

5k Same  as  No.  1 39  6£  66 

5i....                No.  2 18  14-3  50 

5*....                No.  3 31  21-4  65 

6  ....                No.  1 39  6|  72 

6 No.  2 18*  14-3  61 

6 No.  3 31  21-4  74 

7 No.  1,  much  matted  39*  6i  94 

7  ....                No.  3 31  21-4  86 

7i Copper  glance  and  pyrite  in 

quartz  20*  23'4  54  "    12 

The  area  of  the  heap  is  determined  by  the  position  and 
size  of  the  ground  at  disposal,  and  the  convenience  of  deliver- 
ing the  ore.  Its  width  is  limited  by  the  distance  to  which  the 

*  Estimated 


2 
3 

4 

5 

6 

7 

8 

9 

10 

11 


THE   ROASTING  OF   COFFEE  ORES   IN   LUMP  FORM.  59 

covering  material  can  be  conveniently  thrown  with  a  shovel, 
and  by  the  room  between  the  bents  that  support  the  track. 
24  feet  in  width  by  40  in  length  is  a  very  convenient  size, 
smaller  heaps  demanding  considerably  more  labor  and  fuel  to 
the  ton  of  ore.  With  36  feet  between  the  bents,  an  ample 
border  of  6  feet  will  be  left  on  each  side  of  the  pile  for  col- 
lecting the  fines,  wheeling  the  same  wherever  required,  and 
fully  securing  the  wood-work  against  all  danger  of  fire.  Risk 
from  fire  is  further  obviated  by  elevating  the  foundation  sill 
from  which  the  uprights  arise,  upon  a  wall  of  slag-brick,  3 
feet  or  more  in  height.  A  pile  of  the  dimensions  referred  to, 
24  feet  by  40  feet  square,  and  6  feet  high,  will  contain  about 
240  tons  of  ordinary  ore,  and  should  be  built  in  the  following 
manner : 

The  corners  of  the  rectangular  space  on  which  it  is  to  be 
erected  should  be  indicated  by  stakes,  or,  if  the  same  size  is 
to  be  permanently  retained,  by  large  stones,  or,  better,  blocks 
of  slag,  imbedded  in  the  ground.  The  sides  of  the  area  being 
indicated  by  lines  drawn  on  the  ground  to  guide  the  workman, 
the  entire  space  should  be  covered  evenly  to  the  depth  of  four 
or  six  inches  with  fine  ore  from  the  spalling-shed.  This  layer 
of  sulphides  answers  several  purposes :  in  the  first  place,  it  pre- 
vents the  baking  and  adhering  to  the  ground  of  the  coarser 
ore,  which,  especially  when  much  matte  is  formed,  sticks  to 
the  clayey  soil  to  such  an  extent  as  to  tear  up  and  injure  the 
foundation,  besides  mixing  worthless  dirt  with  the  ore,  and 
causing  a  loss  of  the  latter  when  attempts  at  separation  are 
made.  It  also  forms  a  distinct  boundary  line  between  the 
worthless  and  valuable  materials,  and,  when  left  undisturbed 
during  two  or  three  operations,  becomes  itself  so  thoroughly 
desulphurized  that  the  upper  half  or  more  may  be  scraped  up 
with  shovels  and  added  to  the  roasted  ore,  its  place  being 
filled  by  a  fresh  supply  of  fines.  This  operation  completed, 
the  fuel  is  next  arranged  by  an  experienced  workman  in  a 
regular  and  systematic  manner.  The  quality  and  size  of  the 
wood  is  a  matter  of  some  moment,  and  must  be  determined 
for  each  individual  case,  it  being  evident  that  that  variety  of 
fuel  that  yields  the  greatest  amount  of  heat  for  the  longest 
time  possesses  the  highest  money  value,  provided  the  ore  is  of 


60         MODERN  AMERICAN   METHODS   OF   COPPER  SMELTING. 

such  a  nature  as  to  bear  the  temperature  produced  without 
fusing.  As  most  sulphide  ores  will  not  stand  the  heat  gener- 
ated by  a  thick  bed  of  sound,  dry,  hard  wood,  it  frequently 
happens  that  a  cheaper  variety  answers  the  purpose  better. 
The  outside  border  of  wood  that  corresponds  to  the  edges  of 
the  heap  should  be  of  better  quality,  as  no  such  degree  of  heat 
is  attainable  there  as  in  the  interior  of  the  pile.  Therefore  a 
large  proportion  of  the  bed  may  be  made  up  of  old  rails,  logs, 
gnarled  and  knotted  trunks  that  have  defied  wedge  and  beetle, 
and  such  sticks  of  cord-wood  as  are  daily  thrown  out  from 
wood-burning  boilers  and  calcining-furnaces  as  too  crooked 
and  misshapen  to  enter  a  contracted  fire-place.  Such  miscel- 
laneous fuel  causes  somewhat  greater  labor  in  arrangement ; 
but  whatever  the  material,  it  must  be  placed  with  such  care 
and  skill  as  to  form  a  solid  and  sufficient  bed,  varying  in  depth 
from  8  to  14  inches  according  to  the  behavior  of  the  ore. 
However  rough  and  irregular  the  greater  portion  of  the  fuel 
at  our  disposal  may  be,  enough  cord-wood  of  even  length  and 
diameter  should  be  selected  to  form  a  four-foot  border  around 
the  entire  heap  and  just  within  the  side-lines  of  the  area ;  for 
the  even  and  regular  kindling  of  the  heap  depends  considera- 
bly upon  the  proper  arrangement  of  this  border.  Sticks  of 
cord- wood  not  larger  than  5  inches  in  diameter  should  be 
laid  side  by  side  across  both  ends  and  sides  of  the  area. 
Across  this  layer,  small  wood  is  again  piled  until  this  four-foot 
border  has  been  built  up  to  the  height  of  some  10  inches, 
brushwood  and  chips  being  scattered  over  the  surface  to  fill 
up  all  interstices,  while  canals  6  inches  wide,  filled  with 
kindlings,  are  formed  at  intervals  of  8  or  10  feet,  leading  from 
the  outer  air  and  communicating  with  the  chimneys  in  the 
center  line  of  the  heap.  The  empty  area  within  this  encir- 
cling border  is  now  filled  with  the  poorer  quality  of  fuel,  all 
sticks  laid  parallel  and  with  as  much  regularity  as  possible, 
to  cover  all  cracks  and  interstices,  that  no  ore  may  fall  through 
the  wood,  and  to  cover  over  the  draught-canals  in  such  a  man- 
ner that  they  shall  be  neither  choked  nor  destroyed  by  the 
superincumbent  load.* 

*  An  excellent  paper  on  heap  roasting  in  Vermont,  by  Mr.  William 
Glenn,  may  be  found  in  the  Engineering  and  Mining  Journal  for  Decem- 
ber 8,  1883. 


THE   BOASTING  OF   COPPER  ORES   IN   LUMP   FORM.  61 

The  chimneys,  which  assist  materially  in  rapidly  and  cer- 
tainly kindling  the  entire  heap,  are  formed  of  four  worthless 
boards  nailed  lightly  together  in  such  a  manner  that  two  of  the 
opposite  sides  stand  some  eight  inches  from  the  ground,  thus 
leaving  spaces  that  communicate  with  the  draught-canals 
referred  to,  and  toward  which  several  of  the  latter  converge. 
For  a  heap  40  feet  in  length,  three  such  chimneys,  eight  inches 
square,  will  suffice.  They  should  project  at  least  two  feet  above 
the  proposed  upper  surface  of  the  structure,  that  no  fragments 
of  ore  may  accidentally  enter  the  flue  opening  and  destroy  its 
draught.  In  certain  localities,  where  even  old  boards  are  too 
valuable  to  be  needlessly  sacrificed,  two  or  three  medium-sized 
sticks  of  cord- wood  may  be  wired  together  to  form  the  chim- 
ney ;  or  old  pieces  of  sheet-iron,  such  as  condemned  jig-screens, 
worn-out  corrugated  roofing-iron,  etc.,  may  be  so  bent  and 
wired  as  to  form  a  permanent  and  sufficient  passage,  while  this 
material  will  answer  for  several  operations.  The  chimneys 
being  placed  in  position,  equidistant,  and  on  the  longitudinal 
center  line  of  the  bed  of  fuel,  and  held  upright  by  temporary 
wooden  supports,  the  heap  is  ready  to  receive  the  ore.  This 
is  brought  in  car-loads  of  1,500  or  2,000  pounds  from  the 
spaUing-shed,  and  weighed  en  route  on  track-scales.  It  is 
dumped  on  a  portable  wooden  platform  about  eight  feet  square, 
to  prevent  the  deranging  of  the  wood  from  the  fall  of  so  heavy 
a  mass  of  rock  from  a  height  of  ten  feet  or  thereabout.  The 
first  few  car-loads  are  heaped  about  the  chimneys,  and  the 
platform  is  changed  from  place  to  place  as  convenience  de- 
mands, until  the  bed  of  wood  is  thoroughly  protected  by  a 
thick  layer  of  ore.  The  remainder  of  the  process  is  a  very 
simple  operation.  The  cars  of  ore  are  dumped  in  turn  over 
the  entire  area  by  a  systematic  shifting  of  the  temporary  pair 
of  rails  already  described,  and  the  heap  formed  into  a  shapely 
pyramid  with  sharp  corners  and  an  angle  of  inclination  of 
some  42  degrees,  or  as  steep  as  the  ore  will  naturally  lie  with- 
out rolling.  The  main  body  of  the  structure  is  formed  of  the 
coarsest  class  of  ore  ;  the  ragging  is  next  placed  upon  the  pile, 
forming  a  comparatively  thick  covering  at  the  part  nearest  the 
ground,  and  gradually  thinning  out  toward  the  top  and  on  the 
upper  surface.  Its  thickness  depends  on  the  amount  available, 


62        MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

and  no  fears  need  be  entertained  of  its  having  an  unfavorable 
influence  on  the  calcination ;  for  when  carefully  separated 
from  the  finest  class,  a  heap  formed  entirely  of  ragging  will 
give  reasonably  good  results.  The  extreme  outside  edge  of 
the  ore,  when  all  is  in  place,  should  not  entirely  cover  the 
external  border  of  wood.  At  least  a  foot  of  uncovered  fuel 
should  project  beyond  the  layer  of  ragging,  both  to  prevent  the 
ore  from  sliding  off  its  bed  as  well  as  to  insure  a  thorough 
kindling  of  the  outer  covering  of  mineral.  The  amount  of 
wood  required  properly  to  burn  a  heap  of  240  tons  of  ore  will 
vary  greatly  with  the  composition  of  the  latter,  standing  in 
direct  proportion  to  its  sulphur  contents,  and  especially  to  the 
amount  of  bisulphides  present,  but  may,  on  the  average,  be 
estimated  at  12  cords,  or  one  cord  of  wood  to  20  tons  of 
ore.  In  smaller  heaps,  this  proportion  must  be  considerably 
increased. 

The  fine  ore  that  is  to  form  the  external  layer,  and  on  which 
depends  largely  the  success  of  the  process,  is  seldom  placed 
upon  the  heap  until  after  it  is  fired.  Perhaps  the  most 
judicious  practice  is  to  cover  the  sides  of  the  pile  with  a  very 
thin  layer,  scattering  it  evenly  with  a  shovel,  and  leaving  the 
upper  surface,  as  well  as  a  space  eighteen  inches  broad  at  the 
bottom,  uncovered ;  for  if  the  fine  ore  is  thrown  carelessly  upon 
the  lower  circumference  of  the  pile,  the  draught  is  decidedly 
hampered  and  the  fire  stifled  before  getting  fairly  under  way. 
For  an  average  ore,  an  amount  of  fines  equal  to  10  per  cent,  of 
its  total  weight  is  ample ;  of  this,  eight  tons  may  be  strewn 
lightly  upon  the  sides  of  the  heap,  as  just  described,  the 
remaining  16  tons — assuming  the  entire  contents  to  be  240 
tons — being  arranged  in  small  piles  upon  the  empty  space  be- 
tween the  roast-heaps,  where  it  is  easily  accessible  to  the 
shovel.  The  lighting  should  be  done  just  as  the  day  shift  is 
quitting  work,  as  the  dense  fumes  of  wood  smoke,  strongly 
saturated  with  pyroligneous  acid  and  the  various  gaseous  com- 
pounds of  sulphur  and  arsenic,  among  which  sulphureted 
hydrogen  is  always  plainly  distinguishable,  are  almost  unbear- 
able. 

If  possible,  fine  weather  should  be  selected  for  this  pur- 
pose ;  for  although  no  rain,  however  violent,  is  capable  of  ex- 


THE   BOASTING  OF   COPPER   ORES   IN   LUMP  FORM.  63 

tinguishing  a  well-lighted  roast-heap,  it  may  still  interfere 
greatly  with  kindling  a  new  one,  and  is  quite  likely  to  cause 
subsequent  irregularities  in  the  course  of  the  process.  There 
are  several  different  methods  of  firing  a  roast-heap — such  as 
lighting  it  only  on  the  leeward  side,  and  letting  the  fire  creep 
back  against  the  wind,  kindling  it  through  the  draught-chim- 
neys, etc.,  each  of  which  has  its  advocates  among  roasting 
foremen ;  but  long-continued  observation  has  shown  that  no 
advantage  is  gained  by  any  of  these  irregular  methods,  and 
the  most  sensible  and  successful  practice  is  to  light  it  as 
quickly  and  thoroughly  as  possible  by  applying  a  handful 
of  cotton  waste,  saturated  with  coal  oil,  or  a  ladle  of  molten 
slag,  to  the  kindling-wood  at  the  mouth  of  each  of  the 
draught-canals,  these  being  some  six  or  eight  in  number,  as 
already  described.  As  the  success  of  the  entire  operation  de- 
pends principally  on  the  management  of  the  heap  for  the  first 
few  days  after  kindling,  it  will  be  necessary  to  study  some- 
what in  detail  the  phenomena  that  it  should  normally  exhibit 
during  this  critical  period,  always  bearing  in  mind  the  impos- 
sibility of  laying  down  any  fixed  rules  that  shall  apply  to  all 
circumstances  and  to  every  variety  of  material. 

Under  ordinary  circumstances,  the  heap  may  best  be  left 
entirely  to  itself  for  from  four  to  six  hours  after  lighting,  care 
merely  being  taken  that  the  kindling  burns  freely,  and  that 
the  draught-holes  communicate  with  their  respective  chimneys. 
At  the  expiration  of  this  time,  if  the  fire  has  spread  well  over 
the  entire  area,  about  one-half  of  the  remaining  fines  that  have 
been  provided  for  covering  should  be  scattered  lightly  upon  the 
heap  ;  the  lower  border  and  upper  surface,  which  have  hitherto 
been  left  unprotected,  now  receive  a  thin  application,  while 
the  lateral  coating  is  rendered  somewhat  thicker  and  more 
impervious.  If  matters  pursue  a  normal  course,  the  early 
morning — twelve  hours  after  firing — should  see  the  heap  smok- 
ing strongly  and  equally  from  innumerable  interstices  produced 
by  the  settling  of  the  whole  mass,  due  to  the  disappearance  of 
the  thick  foundation  of  fuel.  Dense  pillars  of  opaque,  yellow 
smoke,  smelling  strongly  of  sulphurous  acid,  arise  from  the 
site  of  each  chimney ;  although  if  these  were  constructed  of 
wood,  no  sign  of  them  will  remain  except  a  few  charred  frag- 


64       MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

ments,  resting  in  a  slight  depression,  which  marks  their  sites. 
The  entire  surface  will  be  found  damp  and  sticky,  and  the 
covering  material  will  have  already  formed  quite  a  perceptible 
crust,  from  the  adhesion  of  its  particles.  This  "  sweating,"  as 
it  is  termed,  arises  from  the  distillation  products  of  the  fuel — 
owing  to  its  very  imperfect  combustion — and  from  the  mois- 
ture contained  in  the  ore.  A  yellowish  crust  surrounding  the 
vents  from  which  the  strongest  currents  of  gas  are  seen  to 
issue  indicates  the  presence  of  metallic  sulphur,  the  volatiliza- 
tion of  the  first  loosely  bound  atom  of  which  begins  soon  after 
the  wood  is  fairly  lighted.  Its  quantity  depends  on  the  pro- 
portion of  bisulphides  in  the  roast,  as  well  as  on  the  freedom 
with  which  air  is  admitted  ;  the  scarcity  of  oxygen  and  a 
rather  low  degree  of  heat  favoring  its  direct  volatilization, 
while  an  abundance  of  air  and  a  comparatively  elevated  tem- 
perature influence  the  plentiful  generation  of  sulphurous  acid. 
During  this  first  day,  the  newly  kindled  heap  will  require 
close  and  constant  attention  to  prevent  any  undue  local  heat- 
ing ;  nor  is  it  at  all  uncommon  to  find  that  some  neglected  fis- 
sure has  increased  the  draught  to  such  an  extent  as  to  cause 
the  sintering  or  partial  fusion  of  several  tons  of  ore  at  that 
point.  The  principal  signs  by  which  the  experienced  eye 
judges  of  the  condition  of  affairs  are  the  color  of  the  gas  and 
the  rapidity  with  which  it  ascends ;  the  amount  of  settling  and 
consequent  fissuring  of  the  covering  layer;  and,  above  all, 
the  degree  of  heat  at  different  parts  of  the  surface.  A  light, 
bluish  gas,  nearly  transparent,  and  ascending  in  a  rapid  cur- 
rent, is  a  sign  that  the  heat  is  too  great  at  that  point,  and  the 
admission  of  air  too  free.  The  fissuring  of  the  crusted  cover- 
ing material,  after  the  general  and  extensive  sinking  caused  by 
the  consumption  of  the  fuel,  indicates  a  rapid  settling  that  can 
only  arise  from  the  melting  together,  and  consequent  contrac- 
tion, of  the  lumps  of  ore.  Ah1  these  conditions  are  met  by  a 
single  remedy ;  that  is,  covering  the  surface  at  that  point  more 
thoroughly  with  fines,  by  which  means  the  air  is  excluded, 
the  rapidity  of  the  oxidation  process  diminished,  and  the 
temperature  lowered.  It  should  not  be  supposed  that,  because 
the  interstices  that  exist  in  the  upper  part  of  the  heap  alone 
show  evidences  of  heat  and  gas,  those  cracks  and  openings 


THE   ROASTING  OF  COPPER  ORES   IN  LUMP  FORM.  65 

that  have  been  left  nearer  the  ground  are  of  no  importance  ; 
these  are  the  draught-holes,  while  the  former  constitute  the 
chimneys,  and  it  is  to  the  condition  of  the  lower  border  of  the 
pile  that  our  attention  should  be  most  frequently  directed  in 
regulating  the  proper  admission  of  air.  A  few  shovelfuls  of 
fine  ore  judiciously  applied  at  the  base  of  the  heap  will  often 
have  more  effect  than  a  car-load  scattered  aimlessly  over  the 
surface. 

Only  an  experienced  laborer  can  manage  a  roast-heap  to 
the  best  advantage,  nor  is  it  possible  to  establish  fixed  rules 
for  the  guidance  of  this  process,  varying  conditions  demand- 
ing totally  different  treatment.  In  a  general  way,  it  may  be 
said  that,  after  somewhat  subduing  the  intense  heat  caused  by 
the  sudden  combustion  of  so  large  an  amount  of  wood,  the 
attendant  should  confine  himself  to  scattering  the  covering 
material  in  a  thin  layer  over  the  sides  and  top  of  the  struct 
ure,  and  effectually  stopping  up  such  holes  and  crevices  as 
seem  to  be  the  vents  for  some  unusually  heated  spot  below. 

By  the  third  day  large  quantities  of  sublimated  sulphur  will 
be  found  upon  the  surface,  in  many  places  melting  and  burn- 
ing with  a  blue  flame.  It  is  now  necessary  for  the  attendant 
to  ascend  to  the  top  of  the  heap,  to  properly  examine  the 
upper  surface,  and  place  additional  covering  material  on  such 
portions  as  still  seem  too  hot.  In  doing  this,  a  disagreeable 
obstacle  is  encountered  in  the  clouds  of  sulphurous  gas,  which, 
to  one  unaccustomed  to  the  task,  seem  absolutely  stifling. 
By  taking  advantage  of  their  momentary  dispersion  by  cur- 
rents of  air,  and  retreating  when  they  become  too  thick,  no 
difficulty  need  be  experienced  in  covering  the  upper  surface  of 
the  heap  as  thoroughly  and  carefully  as  any  other  part  of  it. 

If  the  process  of  combustion  seems  to  have  spread  equally 
to  all  parts  of  the  pile,  nothing  need  now  be  done  except  daily 
to  scatter  a  few  shovelfuls  of  fines  over  such  heated  spots  as 
seem  to  require  it ;  but  if  any  isolated  corner  of  the  heap  has 
failed  to  kindle,  or,  having  once  caught  fire,  has  now  become 
cold  and  ceased  to  smoke,  it  is  necessary  to  draw  the  fire  in 
that  direction.  This  can  be  accomplished  with  ease  and  cer- 
tainty by  any  one  accustomed  to  the  work ;  for  there  is  no 
danger  of  a  roast-heap  becoming  extinguished  when  once 
5 


66       MODERN  AMERICAN   METHODS   OF   COPPER  SMELTING. 

fairly  kindled.  Certain  isolated  spots — especially  corners  and 
angles — may  fail  to  become  properly  ignited,  but  by  opening 
a  few  draught-holes  in  the  neighborhood  the  fire  will  surely 
spread  wherever  unburned  sulphides  still  exist.  Beginning  at 
the  end  of  the  first  week,  and  continuing  for  a  month  or  more, 
a  certain  amount  of  sulphur  may  be  obtained  by  forming  18 
or  20  circular,  ladle-shaped  holes  about  14  inches  in  diameter 
and  7  inches  deep  in  the  upper  surface  of  the  heap,  and  lining 
them  carefully  with  partially  roasted  fine  ore,  so  that  they 
may  retain  the  molten  metalloid.  The  impure  sulphur  may 
be  ladled  out  twice  a  day  into  wooden  molds ;  but  the  impurity 
of  the  product,  caused  by  the  great  quantity  of  ore-dust  and 
cinders  constantly  falling  into  the  melted  material,  and  the  ex- 
tremely scant  production  of  a  substance  that  is  hardly  worth 
saving,  discourages  the  general  adoption  of  the  practice, 
although  at  some  of  the  older  German  works  it  is  still  kept  up. 
Experiments  made  with  the  greatest  possible  care  saved  only 
one-tenth  of  one  per  cent,  of  the  total  weight  of  the  ore  from 
a  30  per  cent,  bisulphide  ore. 

With  certain  varieties  of  ore,  the  sulphur,  instead  of  col- 
lecting in  a  concentrated  form  at  the  principal  issuing  vents  of 
the  strongest  currents  of  gases,  condenses  over  the  entire  sur- 
face in  a  thin  layer,  and  upon  melting  cements  and  aggluti- 
nates the  fine  particles  of  the  covering  layer  in  such  a  manner 
as  to  form  an  almost  impermeable  envelope.  In  such  cases 
this  crust  must  be  destroyed,  from  time  to  time,  with  an  iron 
garden-rake,  or  the  process  of  calcination  may  be  delayed  for 
weeks  beyond  its  customary  limit  from  the  lack  of  sufficient 
oxygen  to  maintain  the  proper  rate  of  combustion.  If  arsenic 
is  present,  even  in  the  smallest  quantities,  it  will  soon  make 
itself  visible  as  beautiful  orange-colored  realgar,  AsS,  and  mi- 
nute clusters  of  white,  glistening  crystals  of  arsenious  oxide, 
which  usually  form  at  the  upper  orifices  of  the  accidental 
draught-canals  that  communicate  with  the  interior  of  the 
heap. 

A  strong  and  persistent  wind  from  any  one  direction  has 
an  unfavorable  effect  on  the  process  of  heap-roasting,  driving 
the  fire  toward  the  leeward  side,  and  cooling  those  portions 
that  feel  the  direct  influence  of  the  air-current  to  such  an  ex- 


THE  BOASTING  OF  COPPER  ORES  IN   LUMP  FORM.  67 

tent  that  one-fourth  or  more  of  the  heap  may  remain  in  a  raw 
condition.  It  is  a  somewhat  remarkable  fact  that,  while  it  is 
almost  impossible  to  quench  a  roast-heap  with  water,  unless 
completely  flooded  for  a  considerable  length  of  time,  a  simple 
excess  of  the  very  element  most  favorable  to  its  perfect  com- 
bustion should  have  the  power  to  extinguish  it.  If  this  annoy- 
ing circumstance  repeats  itself  with  any  frequency,  it  will  be 
necessary  to  erect  a  high  board  fence  on  that  side  of  the  yard 
whence  the  most  persistent  winds  prevail.  Rain  and  snow 
have  little  influence  on  the  course  of  the  process,  except  in  so 
far  as  they  may  cause  serious  chemical  and  mechanical  losses. 
It  is  only  after  a  heavy  shower  or  sudden  thaw  that  the  great 
advantage  of  numerous  and  well-preserved  ditches  surround- 
ing the  entire  area,  and  even  leading  between  the  heaps  them- 
selves, is  fully  realized  and  appreciated.  When  wet  weather 
supervenes,  after  a  long  period  of  drought,  the  amount  of  cop- 
per dissolved  from  the  soluble  sulphate  salts  formed  during 
the  extended  term  of  dryness  may  be  so  large  as  to  repay 
some  efforts  to  recover  it.  By  simply  leading  the  drainage 
from  the  roast-yard  into  two  old  brewer's  vats  partially  filled 
with  scrap-iron,  during  one  summer,  3,546  pounds  of  40  per 
cent,  precipitate  were  collected. 

During  the  last  two-thirds  of  the  life  of  the  roast-heap  it 
hardly  requires  an  hour's  labor,  and  if  the  works  possess  an 
ample  stock  of  roasted  ore  in  advance,  nothing  further  need 
be  done  to  the  pile  until  it  has  burned  itself  out  and  becomes 
sufficiently  cool  to  handle.  The  daily  inspection,  however, 
should  never  be  omitted ;  for  even  at  this  advanced  stage  of 
the  process,  irregular  settling  or  swelling  of  some  portion  of 
the  structure  may  cause  sufficient  fissuring  and  consequent 
admission  of  air  to  produce  serious  matting,  a  disaster  that 
the  application  of  a  single  shovelful  of  fines  at  the  beginning 
of  the  trouble  would  have  prevented.  In  fact,  it  is  far  better 
to  leave  the  heap  undisturbed,  unless  good  reasons  exist  for 
breaking  into  it,  as  the  agglutinated  covering  material  forms  a 
roof  almost  impermeable  to  rain  and  wind,  while  the  freshly 
calcined  ore,  when  exposed  to  these  elements,  necessarily  un- 
dergoes a  serious  waste.  But  if,  as  is  in  most  instances  the 
case,  the  demand  for  ore  from  the  smelting  department  ex- 


68       MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

ceeds  the  supply  from  the  mine,  but  scant  time  can  be  afforded 
to  the  intermediate  steps,  and  the  calcination  must  suffer.  If, 
therefore,  it  is  the  object  to  utilize,  at  the  earliest  possible 
moment,  the  ore  that  is  stored  up  in  the  heaps,  the}7  should  be 
closely  watched,  and  whatever  portions  of  the  same — usually 
the  ends  and  corners — are  found  to  be  moderately  cool,  should 
be  carefully  stripped  and  broken  into,  the  object  being  to  cool 
the  ore  that  is  already  roasted,  and  extinguish  the  last  remains 
of  fire  as  rapidly  as  possible,  without  interfering  too  seriously 
with  the  process  of  oxidation  that  is  continuing  in  the  main 
body  of  the  pile.  This  is  accomplished  by  digging  away  the 
calcined  ore,  and  following  up  the  line  of  fire  as  it  recedes 
from  the  surface  toward  the  center,  without  approaching  it  so 
closely  as  to  completely  extinguish  it  in  that  portion  of  the 
ore  not  yet  properly  calcined,  which  is  easily  done  at  this 
stage  of  the  operation.  At  least  12  inches  should  be  left  be- 
tween the  outer  air  and  the  line  of  active  oxidation,  and  it  is  a 
good  practical  rule  never  to  allow  the  surface  to  become  so  hot 
as  to  be  unbearable  to  the  naked  hand. 

The  too  common  practice  of  keeping  the  smelting  depart- 
ment so  far  in  advance  of  the  ore  supply  as  to  require  the 
breaking  into  and  utilization  of  roast-heaps  in  which  the  ore 
is  still  red-hot,  and  just  at  the  most  active  and  profitable  stage 
of  calcination,  necessitates  the  employment  of  a  strong  body 
of  laborers  to  bring  water  and  constantly  drench  the  smoking 
ore,  in  order  to  make  it  at  all  possible  for  the  other  workmen 
to  shovel  it  into  their  barrows,  and  must  be  condemned  as  un- 
necessary and  productive  of  more  trouble  and  expense  than 
almost  any  other  practice  at  our  smelting- works. 

Among  these  sources  of  extra  expense  are,  the  doubled  cost 
of  taking  down  and  transporting  the  roasted  material;  the 
burning  and  rapid  destruction  of  tools  and  cars ;  the  medical 
bills  claimed  by  the  workmen  who  suffer  from  such  unhealthy 
employment ;  and,  far  greater  than  all,  the  injurious  effect  on 
all  subsequent  steps  of  the  process,  which  will  be  referred  to 
in  the  chapter  on  Smelting  in  Blast-Furnaces. 

On  the  other  hand,  the  only  possible  advantage  that  can  be 
claimed  is,  that  some  two  or  three  weeks'  interest  on  the  value 
of  the  ore  is  saved. 


THE  ROASTING  OF  COPPER  ORES   IN  LUMP  FORM.  69 

When  the  heap  is  properly  cooled,  the  mass  of  ore,  which, 
while  still  hot,  is  often  almost  as  hard  and  tough  as  a  wall  of 
solid  rock,  crumbles  to  pieces  with  a  single  blow  of  the  pick, 
and  is  wheeled  in  barrows  from  the  roast-heap  to  the  furnace- 
car. 

When  the  heap  is  sufficiently  cooled,  it  is  "  stripped "  by 
removing  not  only  the  fines  that  formed  its  cover,  but  its  entire 
surface  to  such  a  depth  as  is  necessary  to  include  all  material 
that  has  escaped  oxidation.  This  unroasted  material  is  made 
up  largely  of  the  fines  forming  the  cover,  and  which,  though 
often  quite  thoroughly  oxidized  on  the  top  of  the  pile,  are  so 
agglutinated  with  sulphur  as  to  be  unfit  for  the  furnace.  The 
covering  of  the  sides  is  seldom  sufficiently  roasted,  and  this  is 
especially  the  case  near  the  ground,  where  the  ragging  itself, 
to  a  depth  of  several  inches,  is  frequently  found  unscathed. 
The  angles  of  the  pile  are  also  seldom  in  good  condition,  and 
many  isolated  patches  and  bunches  of  ore  will  be  found  that 
the  careful  foreman  will  reject.  This  statement,  however,  refers 
rather  to  the  results  of  the  ordinary  practice  than  to  those  that 
can  easily  be  obtained  by  close  attention  to  details  and  by  en- 
listing the  interest  of  some  intelligent  foreman.  As  already 
explained,  the  fire  will  find  its  way  to  every  nook  and  corner 
where  sulphides  still  exist,  if  only  the  conditions  are  favorable. 
The  author  recollects  with  satisfaction  the  mortification  dis- 
played by  his  roasting  foreman  but  a  few  months  ago,  at  the 
unusual  occurrence  of  a  few  hundredweight  of  fused,  and  a  still 
smaller  amount  of  raw,  ore  in  a  heap  of  some  200  tons. 

A  half-fused,  honey-combed  condition  of  the  upper  part  of 
the  heap,  presenting  the  appearance  of  a  skeleton  of  gangue 
from  which  all  mineral  has  been  melted  out,  is  a  certain  indi- 
cation of  a  proportional  amount  of  matte  below.  This  molten 
material  naturally  gravitates  to  the  bottom  of  the  heap,  and  is 
there  found  in  masses  of  greater  or  less  extent ;  often  of  many 
tons'  weight,  though,  in  such  a  case,  warning  would  have  been 
given  during  the  roasting  by  the  irregular  sinking  of  the  heap, 
and  even  by  depressions  and  crater-like  cavities  on  the  surface. 
This  molten  product  is  very  properly  termed  "  heap-matte," 
and  varies  neither  in  appearance  nor  composition  from  the  sim- 
ilar product  of  a  blast-furnace.  A  popular  impression  prevails 


70        MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

among  certain  foremen,  and  even  assay  ers,  that  the  light  honey- 
combed material  that  remains  after  the  melting  out  of  its  sul- 
phide constituents  is  rich  in  copper,  but  the  contrary  is  true. 
The  unfused  skeleton  merely  represents  the  siliceous  slag, 
while  the  molten  sulphide  mass  below  is  the  equivalent  of  the 
matte,  the  purity  and  value  of  either  product  depending  on  the 
temperature  to  which  the  ore  has  been  subjected,  and  the  con- 
sequent perfection  of  the  smelting  or  liquidation  process.  This 
fact  is  sustained  by  the  following  assays  of  samples  of  consid- 
erable size : 

No.  1.  No.  2. 

Original  ore  before  roasting 21  '6  copper.  18'6  copper. 

Siliceous  skeleton 7'3       "  6'4       " 

Heap-matte 347       "  36'6 

The  formation  of  this  heap-matte  in  any  considerable  quan- 
tity is  very  detrimental  to  the  roasting  process,  but  is  easily 
avoidable ;  for  it  is  invariably  caused  by  either  too  much  or 
too  little  air.  In  too  many  instances,  no  particular  notice  is 
taken  of  its  occurrence,  and  it  is  sent  to  the  smelting-furnace 
mixed  with  the  well-roasted  ore.  This  is  exceedingly  bad 
practice,  and  should  on  no  account  be  permitted,  as  it  is  totally 
impossible  to  foresee  the  grade  of  matte  that  will  be  produced 
by  the  smelting  process  when  this  unroasted  sulphide  is  mixed 
in  unknown  and  varying  quantities  with  the  properly  prepared 
charge.  If  the  percentage  of  the  furnace  mixture  be  such  that 
the  addition  of  this  raw  matte  does  not  lower  the  tenor  of  the 
product  below  the  desired  standard,  it  may  then,  of  course,  be 
fed  with  the  roasted  ore,  but  should  be  kept  strictly  by  itself, 
and  added  to  each  charge  in  weighed  quantities.  Any  infringe- 
ment of  this  rule  gives  rise  to  the  formation  of  a  matte  varying 
greatly  in  its  percentage  of  copper  as  well  as  in  its  entire 
composition,  and  deranges  not  only  the  smelting  process,  but 
seriously  affects  the  regularity  of  the  matte  concentration  oper- 
ations. 

The  heap-matte  may  occur  in  such  masses  that  serious  dif- 
ficulty is  experienced  in  breaking  it  up,  especially  as  it  retains 
its  heat  for  a  great  length  of  time,  and  in  this  condition  is 
almost  malleable,  yielding  and  flattening  under  the  blows  of 


THE  BOASTING  OF   COPPER  ORES   IN  LUMP  FORM.  71 

the  sledge  like  a  block  of  wrought-iron.  Much  expense  and  an- 
noyance may  be  spared  by  stripping  the  central  molten  mass 
thoroughly  of  all  adhering  ore,  and  allowing  it  to  cool  for  two 
or  three  days ;  at  the  expiration  of  which  time  it  will  be  found 
quite  brittle  and  comparatively  easy  to  deal  with.  Thorough 
and  repeated  drenchings  with  water  will  produce  even  better 
results ;  but  it  should  be  borne  in  mind  that  a  considerable 
proportion  of  the  cupriferous  contents  of  calcined  ore  is  in  a 
soluble  condition. 

When,  through  carelessness  or  inexperience,  heap-matte  is 
formed,  it  must  be  either  treated  together  with  the  matte  pro- 
duced from  the  first  fusion  in  the  blast-furnace,  or  set  one  side 
until  a  sufficient  amount  is  collected  to  form  a  small  heap  by 
itself,  and  be  re-roasted.  It  should,  on  no  account,  be  mixed 
with  the  raw  ore,  as  it  demands  a  different  treatment,  and  will 
either  cause  irregularities  in  the  ore-roasting,  or  will  pass 
through  that  process  unaltered  and  with  no  perceptible  dim- 
inution in  its  percentage  of  sulphur. 

The  proportion  of  strippings  and  other  unfinished  products 
of  heap  roasting  that  may  be  considered  allowable  was  de- 
termined experimentally  by  simply  weighing  the  finished  and 
unfinished  portions  of  half  a  dozen  consecutive  roast-heaps, 
averaging  about  240  tons  each.  About  10  per  cent,  of  fines 
were  used  for  the  covering  layer  in  each  case.  The  total 
amount  of  unroasted  material,  as  given  in  the  following  table, 
shows  that  even  a  portion  of  the  fines  is  thoroughly  oxidized : 

Unroasted.  Roasted.         Days  heap  was 

Per  cent.  Per  cent.  active. 

90-4  64 

93-4  71 

91-6  70 

91-0  61 

92-4  67 

88-6  57 

The  figures  have  been  slightly  corrected,  without  alter- 
ing their  relative  values,  to  make  the  aggregate  in  each 
case  exactly  equal  100  per  cent.,  which,  of  course,  can  never 
be  precisely  attained  by  adding  the  weights  as  actually 
arrived  at. 


2     

....                66 

3  

8-4 

4  

9-0 

5     

7'6 

6  . 

11-4 

72        MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

While  these  results  are  taken  from  ordinary  every-day 
work,  it  should  be  understood  that  they  can  only  be  attained 
by  the  most  careful  attention  in  the  roasting-yard.  The 
proportion  of  the  product  rejected  as  unfit  for  the  smelting- 
furnace  at  some  works  might  be  even  less  than  in  the  cases 
just  cited,  and  the  reason  may  be  readily  recognized  in  the  low 
grade  of  the  product  from  the  fusion,  and  the  constant  com- 
plaints of  the  impossibility  of  keeping  the  matte  up  to  the 
proper  standard.  A  selection  in  such  cases  as  rigid  and 
thorough  as  in  those  just  tabulated  would  result  in  the  rejec- 
tion of  from  25  to  60  per  cent,  of  the  entire  heap.  An  allow- 
ance of  10  per  cent,  may  therefore  be  considered  reasonable — 
although  demanding  more  than  ordinary  care  and  skill — and 
of  this  three-fourths  should  be  fines.  The  stripping  should  be 
performed  in  a  cleanly  and  systematic  manner,  and  to  an 
extent  several  feet  in  advance  of  the  line  of  excavation,  and 
the  material  thus  removed  piled  on  one  side  to  be  subse- 
quently screened  on  the  first  calm  day ;  for  the  least  wind 
causes  a  heavy  loss  when  handling  this  half-oxidized  powder. 
The  fine  part  is  again  used  as  a  covering,  for  which  it  is 
much  better  suited  than  raw  ore,  while  the  much  smaller 
coarse  portion  is  added  to  the  nearest  heap  in  process  of 
erection. 

It  will  be  readily  seen  that  very  much  more  fine  ore  is  pro- 
duced during  the  processes  of  mining  and  crushing  than  can 
be  used  for  the  purpose  of  covering  material,  especially  as 
only  a  small  proportion  of  the  latter  is  sufficiently  oxidized  at 
each  operation  to  be  passed  on  to  the  smelting-furnace.  The 
problem  of  the  best  means  of  utilizing  this  constantly  increas- 
ing amount  of  fine  ore  in  works  unprovided  with  calcin- 
ing-furnaces  is  often  a  pressing  one.  It  will  be  referred  to 
again,  under  the  heading,  "The  Treatment  of  Pulverized 
Ores." 

The  roast-heap,  when  once  tolerably  cool,  is  torn  down  and 
loaded  into  the  furnace-car  with  great  celerity.  Three  or  four 
men  trundle  the  barrows,  while  double  that  number  wield  the 
pick,  shovel,  and  hammer.  It  is  the  duty  of  these  laborers  to 
break  all  partially  fused  masses  or  lumps  that  are  too  large  for 
proper  smelting  into  fragments  of  a  reasonable  size,  as 


THE  BOASTING  OF   COPPER  OEES   IN  LUMP  FORM.  73 

especially  determined  by  the  metallurgists.  There  is  not  time, 
or  space,  or  opportunity  on  the  charging-floor  of  a  blast-fur- 
nace in  full  operation  to  attend  to  any  duties  beyond  those 
immediately  connected  with  weighing  the  charge  and  filling 
the  furnace,  and  many  serious  irregularities  in  the  smelting 
may  be  traced  to  an  omission  of  this  simple  and  obvious  pre- 
caution. 

A  careful  and  humane  foreman  can  do  much  to  mitigate 
the  annoyance  and  suffering  to  which  the  workmen  are  sub- 
jected during  the  labor  of  tearing  down  a  heap,  by  moving  the 
point  of  attack  from  one  to  the  other  side  of  the  pile,  accord- 
ing to  the  direction  of  the  wind,  as  well  as  by  keeping  the 
fresh  surface  on  which  the  men  are  engaged  well  sprinkled 
with  water,  to  settle  the  fine  ore-dust.  At  best,  this  labor  is 
the  most  disagreeable  and  wearing  connected  with  ordinary 
smelting,  and  no  laborer  should  be  kept  at  such  employment 
for  more  than  three  or  four  days  in  the  week,  and  should  be 
changed  to  some  other  task  during  the  remaining  time.  Aside 
from  the  common  tools  already  enumerated,  long,  stout  steel 
gads  and  a  few  heavy  sledges  are  needed  to  break  up  the  cen- 
tral portion  of  the  structure,  which,  although  not  fairly  fused, 
is  often  so  stuck  together  as  to  require  considerable  labor  for 
its  removal.  At  no  other  work  are  shovels  so  rapidly  de- 
stroyed, and  it  is  to  this  place  that  all  partially  worn,  though 
still  serviceable,  tools  are  sent  to  terminate  their  exist- 
ence. 

After  the  complete  removal  of  the  old  heap  and  any  slight 
repairs  that  may  be  required  to  restore  the  ground  to  its 
former  level,  a  thin  layer  of  raw  fines  is  again  spread  on  the 
old  spot,  and  the  fuel  arranged  for  a  fresh  pile.  The  estimate 
of  costs  for  this  process,  as  given  below,  is  based  on  the  treat- 
ment of  a  very  large  amount  of  ores,  varying  greatly  in  compo- 
sition, and  under  very  various  circumstances,  and  is  purposely 
made  somewhat  liberal  to  allow  for  the  occurrence  of  bad  work 
and  various  other  mishaps  that  are  certain  to  occur  in  a 
greater  or  less  degree.  It  is  based  upon  a  plant  of  100  tons' 
daily  capacity,  and  on  the  assumption  of  only  a  short  dis- 
tance for  transportation  of  the  roasted  ore  to  the  smelting-fur- 
nace  : 


74       MODEEN  AMEEICAN  METHODS  OF  COPPER  SMELTING. 
ESTIMATE,   100  TONS  PEB  24  HOUKS. 

Transportation  to  heaps,  2  men  on  car,  weighing  1  man — 3  men,  at 

$1.50 $4.50 

Labor — Building  and  burning  heaps —  -\ 

4  men,  at  $1.50  =  $6.00           [ 10.00 

2  men,  at  $2.00  =  $4.00  ) 

Fuel  at  the  rate  of  5  cords  per  24  hours  at  $5  a  cord 25.00 

Eemoving  and  loading  roasted  ore,  14  men  at  $1.50 21.00 

1  foreman 2.50 

Transportation  to  furnace  and  weighing  (same  as  to  heap) 4.50 

Oil,  repairs  to  cars,  track,  etc 3.25 

Miscellaneous  labor,  screening,  daily  patching,  etc.,  2  men  at  $1.50. . .  3.00 

Renewing  shovels  and  other  tools 4.00 

Repairs  on  gads,  bars,  and  tools 2.75 

Total $80.50 

Or  80£  cents  a  ton  of  raw  ore.  On  deducting  the  cost  of  the 
double  transportation,  as  well  as  that  portion  of  the  labor 
belonging  to  the  loading  of  the  cars  for  the  smelter,  and  for 
repairs  to  cars  and  track,  etc. — none  of  which  expenses  act- 
ually belong  to  the  process  of  heap  roasting  as  often  esti- 
mated— the  entire  cost  is  at  once  reduced  to  50  cents  a  ton,  or 
thereabout. 

The  degree  of  desulphurization  arrived  at  by  this  process 
is  seldom  accurately  determined,  owing  to  the  difficulty  and 
expense  of  obtaining  an  accurate  sample,  and  to  the  fact  that 
the  experienced  eye  can  very  correctly  judge  of  the  success  of 
the  roast,  while  any  defect  in  the  process  will  become  imme- 
diately apparent  in  the  lowered  tenor  of  the  product  of  the 
succeeding  fusion.  Owing  to  the  scarcity  of  accurate  investi- 
gations on  the  subject,  the  following  determinations  were  made : 

No.  1.  A  heavy  pyritous  ore,  from  the  Ely  mine,  Vermont, 
consisting  principally  of  magnetic  pyrites  and  chalcopyrite. 
Burned  in  a  heap  of  about  300  tons  for  eleven  weeks.  After 
stripping  off  the  surface,  a  sample  of  the  roasted  ore  as  deliv- 
ered at  the  smelting-furnace  was  taken.  The  following  was 
the  assay  of  the  ore  before  and  after  calcination : 

Before  roasting.  After  roasting. 

Sulphur 82'6  per  cent.  7'4  per  cent. 

Copper 8-2       "  9'1 

Insoluble...                             .  27'0       "  311 


THE   BOASTING  OF  COPPER  OEES   IN  LUMP   FORM.  75 

The  condition  of  the  copper  in  the  roasted  sample  was  also 
determined  in  this  case,  as  follows : 

Sulphate  of  copper 1'3  per  cent. 

Oxide  of  copper 2*1         " 

Sulphide  of  copper 5'7        " 

Total 9-1 

No.  2.  A  heavy  pyritous  ore,  being  almost  pure  iron  pyrites 
containing  minute  quantities  of  copper,  silver,  and  gold,  from 
the  Phillips  mine,  Buckskin,  Colorado,  was  roasted  for  6  weeks 
in  piles  of  60  tons,  and  was  used  as  a  flux  for  siliceous  silver 
ores.  A  careful  sample  of  the  roast  yielded  sulphur,  before 
roasting,  46^  per  cent. ;  after  roasting,  11  per  cent. 

A  considerable  number  of  similar  tests  give  corresponding 
results,  showing  that  a  very  fair  degree  of  desulphurization  can 
be  attained  by  this  crude  and  ancient  method,  but  still  better 
results  will  be  reached  in  ores  containing  less  pyrites,  and 
making  the  fact  evident  that,  in  heap  roasting  as  well  as  in  the 
calcination  of  pulverized  sulphides,  the  copper  is  the  last  metal 
present  to  part  with  its  sulphur,  and  that  a  large  proportion  of 
this  still  remains  in  the  condition  of  a  sulphide  after  nearly  the 
entire  iron  contents  have  become  thoroughly  oxidized.  This 
agrees  perfectly  with  all  investigations  relative  to  the  compar- 
ative affinity  of  sulphur  for  the  various  metals,  and  is  in  no 
other  metallurgical  process  more  strikingly  exemplified  than  in 
the  so-called  "  kernel  roasting,"  as  practiced  at  Agordo,  in 
Italy.  There,  the  mechanical  separation  of  the  copper  from 
its  accompanying  pyritous  gangue  is  effected  by  stopping  the 
process  of  calcination  at  the  exact  point  where  the  entire  iron 
contents  have  been  oxidized  into  a  soft  earthy  material,  while 
the  copper  remains  in  combination  with  sulphur  in  a  hard, 
metallic  condition,  and,  most  singularly,  retreats  into  the  center 
of  each  lump  of  ore,  forming  a  heavy  and  solid  kernel,  which 
can  easily  be  separated  from  its  earthy  envelope  by  inexpen- 
sive mechanical  means.  As  this  interesting  process  is  not 
practiced  in  this  country,  and  in  all  probability  is  not  suited 
to  our  domestic  conditions,  the  student  desirous  of  pursuing 
the  subject  will  find  in  Plattner's  Hostprocesse,  as  well  as  in  a 


76        MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

paper  by  the  author  in  the  Mineral  Resources  of  the  United 
States  (A.  Williams,  Jr.,  1883),  further  information. 

The  appearance  of  a  freshly  opened  heap  of  well-roasted 
ore  is  characteristic,  although  difficult  of  description.  It 
should  present  a  strictly  earthy,  irregular  surface  of  a  black- 
ish-brown hue,  the  scarcity  of  air  preventing  the  oxidation  of 
the  iron  to  the  red  sesquioxide.  This  is  a  decided  advantage 
in  a  reverberatory  smelting-furnace,  where  the  powerful  car- 
bonic oxide  atmosphere  of  the  blast-furnace  is  wanting,  to 
reduce  it  to  the  protoxide,  and  thus  fit  it  for  entering  the  slag, 
the  higher  oxide  being  infusible  at  ordinary  smelting  tempera- 
tures. It  is,  in  fact,  principally  a  magnetic  oxide,  and,  while 
the  greater  part  of  the  contents  should  adhere  closely  together, 
and,  when  disturbed,  should  come  out  in  the  shape  of  large 
lumps,  no  sign  of  actual  fusion  should  be  visible,  and  the  largest 
mass  should  fall  into  fragments  at  a  few  blows  of  the  hammer. 
The  more  siliceous  pieces  of  ore  will  have  taken  on  a  somewhat 
milky  and  opaque  look  in  place  of  the  ordinary  vitreous  ap- 
pearance of  quartzose  minerals,  and  the  veinlets  of  sulphides 
traversing  the  same  will  be  found  oxidized  throughout.  The 
solid  lumps  of  pyrites,  if  carefully  broken,  will  usually  display 
a  series  of  concentric  layers,  completely  oxidized  and  earthy 
on  the  outside,  and  gradually  acquiring  greater  firmness  and  a 
slight  sub-metallic  luster,  which  culminates  in  a  rich  kernel 
near  the  center  of  the  fragment.  This  resembles  strongly  one 
or  other  of  the  grades  of  matte  as  produced  from  the  smelting- 
furnace,  and  usually  contains  the  greater  part  of  the  entire 
copper  contents  of  the  lump.  The  silver — if  any  be  present — 
is  also  concentrated  in  a  marked  degree,  though,  so  far  as  the 
author's  own  investigations  extend,  not  with  the  same  remark- 
able perfection  as  the  less  precious  metal.  The  examination  of 
a  characteristic  lump,  such  as  just  described,  which  contained 
before  roasting  about  4  per  cent,  of  copper,  yielded  the  follow- 
ing interesting  results : 

The  outer  earthy  envelope  contained Traces  of  copper. 

The  medium  concentric  layers 1'2  per  cent.          " 

The  central  sub-metallic  kernel 69'6        " 

An  imperfect  roasting  is  quickly  detected  by  the  presence 
of  more  or  less  fused  material  at  certain  portions  of  the  heap, 


THE  BOASTING  OF   COPPER  OEES  IN  LUMP  FORM.  77 

while  elsewhere  there  exists  no  cohesion  between  the  lumps  of 
ore,  which  fall  apart  like  so  many  paving-stones.  A  certain 
metallic  appearance  will  also  be  noticed,  very  different  from 
the  dull,  earthy  character  of  the  properly  burned  pile.  Although 
a  large  proportion  of  the  contents  may  exhibit  quite  a  brilliant 
red  color,  as  though  an  unusually  perfect  oxidation  of  the  iron 
had  taken  place,  a  mere  weighing  of  one  of  the  lumps  in  the 
hand  will  quickly  undeceive  the  least  experienced  observer, 
and  its  fracture  will  show  that  the  effect  of  the  fire  was  only 
surface  deep,  while  the  entire  interior  remains  unaltered.  A 
careful  study  of  different  roast-heaps,  wherever  opportunity 
offers,  will  soon  render  the  student  skillful  in  judging  by  eye 
of  the  degree  of  success  attained  by  this  process,  and  in  after- 
life frequently  furnish  him  the  key  to  the  cause  of  the  unsatis- 
factory tenor  of  the  matte  produced  from  his  furnaces.  No 
metallurgical  process  is  more  dependent  upon  an  efficient  and 
conscientious  foreman,  and  the  best  results  are  usually  obtained 
by  selecting  some  intelligent  and  ambitious  man  from  the  roast- 
yard  laborers,  and  holding  him  strictly  responsible  for  results. 

HEAP  ROASTING  OF  MATTE. 

There  remains  only  in  connection  with  this  portion  of  the 
subject  to  notice  the  slight  deviations  that  it  is  found  neces- 
sary to  introduce  in  adapting  this  method  to  the  treatment  of 
matte. 

These  artificially  formed  sulphides,  containing  variable  per- 
centages of  sulphur,  may  be  sufficiently  desulphurized  in 
heaps,  nor  has  their  chemical  composition  any  marked  effect 
upon  the  result,  provided  lead  is  not  present  to  such  an  extent 
— fifteen  per  cent,  or  more — as  to  increase  the  fusibility  of  the 
material. 

The  most  marked  distinction  between  the  behavior  of  ore 
and  matte,  when  submitted  to  this  process,  is  the  fact  that, 
while  the  former  substance  may  be  satisfactorily  oxidized  by  a 
single  treatment,  the  latter  invariably  demands  two,  and 
oftener  three  or  more,  separate  burnings  before  it  is  properly 
prepared  for  the  succeeding  fusion.  There  is  no  exception  to 
this  rule,  which,  if  properly  understood,  would  prevent  the 
disappointment  frequently  experienced  by  those  unaccustomed 


78        MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

to  this  method  of  desulphurizing  matte,  and  who  are  led  to 
condemn  the  practice  on  finding,  at  the  conclusion  of  the  first 
carefully  conducted  burning,  that  the  only  visible  results  are  a 
slight  scorching  of  the  surface  of  each  fragment,  a  change  in 
color  from  the  original  brownish-black  to  a  brassy  yellow,  and 
a  more  or  less  extended  fusion  of  such  portions  of  the  heap  as 
have  sustained  the  greatest  heat.  In  reality,  the  influence  of 
the  process  has  been  much  more  profound  than  can  be  real- 
ized from  external  appearances,  and  although  neither  the 
removal  of  the  sulphur  nor  the  oxidation  of  the  iron  and 
copper  has  progressed  to  any  great  extent,  a  certain  change  in 
the  physical  condition  of  every  fragment  of  matte  has  been 
effected  that  prepares  it  perfectly  for  a  second  burning,  and 
which  seems  a  necessary  preliminary  to  the  actual  desulphuri- 
zation. 

Each  succeeding  operation  requires  a  slightly  increased 
proportion  of  fuel,  as  the  volatilization  of  the  sulphur  and  the 
oxidation  of  the  metallic  constituents  deprive  the  matte  of  its 
internal  sources  of  heat,  and  at  the  same  time  greatly  lessen  its 
fusibility. 

For  the  first  roasting,  a  bed  of  wood  should  be  prepared 
similar  to  that  for  a  heap  of  ore,  although  smaller  in  area ;  for 
it  is  difficult  to  regulate  the  temperature  and  prevent  matting 
in  a  heap  much  larger  than  twelve  feet  square,  and  this  will 
be  found  a  convenient  size  to  hold  from  sixty  to  seventy  tons 
of  matte  when  raised  to  a  height  of  about  six  feet.  A  single 
chimney  in  the  center  is  sufficient,  and  about  this  structure  the 
broken  matte  should  be  heaped  just  as  it  comes  from  the 
crusher  or  spalling-floor,  and  regardless  of  the  fines  that  it  con- 
tains. The  presence  of  these  has  been  found  necessary  to 
check  the  rapidity  of  the  operation,  and  prevent  the  fire 
from  suddenly  spreading  through  the  entire  pile  in  a  few  hours 
without  accomplishing  any  useful  result,  though  generating  for 
a  short  time  a  temperature  high  enough  to  fuse  a  large  propor- 
tion of  the  contents  into  a  single  lump. 

Less  care  need  be  taken  in  shaping  a  matte-heap  than  in 
the  case  of  ore,  and  it  is  merely  necessary  to  build  it  up  in  the 
form  of  a  rude  mound,  which  may  best  be  covered  with 
thoroughly  burned  ore  from  the  roast-heaps,  most  of  which  on 


THE   BOASTING  OF  COPPER  ORES   IN   LUMP  FORM.  79 

handling  will  crumble  to  a  sufficient  fineness  for  the  purpose, 
while  any  hard  lumps  may  be  removed  with  the  dung-fork. 
This  obviates  any  screening  or  classifying  of  the  matte  in  the 
open  air,  which  always  entails  a  heavy  loss,  owing  to  the  great 
value  and  excessive  friability  and  lightness  of  the  material 
after  calcination.  If,  as  is  usually  the  case,  the  proportion  of 
fines  after  the  first  burning  is  found  so  great  as  to  endanger 
the  proper  combustion  of  the  heap  for  the  second  operation, 
the  mechanical  loss  maybe  reduced  to  a  minimum  by  separat- 
ing the  excess  of  pulverized  matte  by  the  use  of  a  dung-fork, 
with  tines  closely  set,  during  the  turning  of  the  ore  from  the 
heap  just  finished  on  to  the  fresh  bed  of  wood,  and  at  the  con- 
clusion of  the  process,  removing  the  fines  that  are  thus  isolated, 
either  directly  to  the  smelting-house,  or,  if  they  still  contain 
too  much  sulphur,  to  the  calcining-furnaces.  The  covering  of 
the  original  heap,  consisting  solely  of  roasted  ore,  should  be 
stripped  off,  and  either  sent  to  the  smelting-furnace  or  again 
used  for  a  similar  purpose.  It  need  hardly  be  mentioned  that 
the  presence  of  arsenic  or  similar  impurities  in  the  ore,  in 
greater  quantities  than  in  the  matte,  should  prevent  any  such 
practice  as  that  just  recommended,  and  it  may  be  accepted  as 
a  universal  rule  in  copper  smelting  that  no  impure  ores  or  prod- 
ucts should  ever  be  mixed  with  those  freer  from  deleterious 
substances. 

Under  no  circumstances  need  a  matte-pile  be  covered  as 
thoroughly  as  a  roast-heap  consisting  of  ore,  nor  can  the  forma- 
tion of  a  considerable  amount  of  matte,  which  in  ore-roasting 
would  be  evidence  of  a  great  want  of  skill  or  care,  be  consid- 
ered as  a  reproach,  experience  having  so  conclusively  shown 
the  impossibility  of  preventing  its  occurrence  that,  unless 
about  -J  of  the  lower  portion  of  a  matte-heap  is  thus  fused,  no 
thorough  oxidation  of  the  remainder  will  be  effected.  The 
time  necessary  for  the  operations  just  discussed  varies  accord- 
ing to  the  quality  of  the  matte,  the  condition  of  the  weather, 
and  certain  other  factors,  but  will  in  general  be,  for  the  first 
burning,  8  days,  while  on  the  tenth  day  the  heap  will  be  suffi- 
ciently cool  to  permit  its  turning  on  to  a  fresh  layer  of  fuel. 
The  second  operation  requires  a  day  longer,  and  the  third  a 
day  less  than  the  first  burning. 


80       MODEEN  AMEKICAN  METHODS   OF  COPPEK  SMELTING. 

To  those  familiar  with  the  practice  of  heap-roasting  as  ap- 
plied to  ores,  no  particular  directions  are  necessary  except  that 
care  should  be  taken  that  the  large  blocks  of  matte  that  are 
formed  during  each  burning  be  well  broken  up  and  placed  near 
the  center  of  the  heap  next  constructed,  that  they  may  have 
every  opportunity  for  a  thorough  desulphurization.  Whatever 
raw  matte  still  remains  from  the  last  burning  is  best  reserved 
until  the  construction  of  a  fresh  heap  furnishes  the  proper 
means  for  its  treatment.  At  the  last  two  burnings,  it  is  well 
to  introduce  two  or  more  layers  of  chips,  bark,  or  other  refuse 
fuel  into  the  matte-heap ;  for  it  will  act  powerfully  in  decom- 
posing the  sulphates  that  at  this  stage  are  formed  in  consider- 
able amount,  and  also  exercise  a  similar  and  most  marked 
effect  on  whatever  compounds  of  arsenic  and  antimony  may  be 
present.  This  simple  measure  had  a  sufficient  effect  in  a  cer- 
tain instance  in  the  experience  of  the  author  to  be  plainly 
noticeable  in  the  quality  of  the  ingot  copper  produced. 

No  attempt  to  select  such  portions  of  thoroughly  calcined 
material  as  will  be  found  after  the  second  burning  has  ever 
proved  remunerative.  The  heap  of  matte  must  be  treated  as 
a  whole,  and  the  roastings  continued  until  the  desired  grade 
of  desulphurization  is  reached. 

The  process  just  described  is  seldom  an  advantageous  one, 
as,  aside  from  the  production  of  the  vilest  fumes  known  to  met- 
allurgy, the  value  of  the  material  operated  on  is  too  great  to 
admit  of  being  locked  up  for  30  days  or  more,  or  to  warrant 
the  loss  that  necessarily  results  from  such  frequent  handling  in 
the  open  air.  The  last  difficulty  may  be  partially  obviated  by 
erecting  a  light  structure  to  protect  the  heaps  from  the  rain  and 
wind ;  but,  at  best,  the  practice  is  an  imperfect  and  objection- 
able one,  and  only  to  be  recommended  in  new,  outlying  districts 
where  an  expensive  calcining  plant  cannot  at  once  be  erected, 
and  where  the  climate  is  favorable  for  out-of-door  operations. 
The  expense  of  crushing  and  calcining  in  furnaces  is  scarcely 
greater  than  the  three  or  four  burnings  necessary  to  produce 
the  same  result ;  but  the  condition  of  the  roasted  material  is 
so  much  more  favorable  for  the  succeeding  smelting  process, 
in  the  case  of  heap  roasting,  that  this  reason  alone  is  often 
sufficient  to  outweigh  all  objections,  that  can  be  offered. 


THE   BOASTING   OF   COPPER  ORES   IN  LUMP   FORM.   ,       81 

The  practice  of  spalling  the  large  pieces  of  matte  upon  the 
heap  itself  must  be  deprecated,  as  it  has  a  strong  tendency 
to  solidify  the  structure  and  render  the  draught  weak  and 
irregular. 

The  cost  of  this  process,  based  upon  the  roasting  of  many 
thousand  tons  of  matte,  and  divested  of  those  details  that  too 
closely  resemble  the  heap-roasting  of  ore  to  warrant  repetition, 
is  as  follows,  assuming  the  daily  amount  of  fresh  matte  subjected 
to  this  treatment  to  average  30  tons : 

COST  PER  TON  OP  MATTE. 

First  Fire. 

Breaking $0.35 

Transportation  to  heap 0.15 

Fuel — allowing  3  cords  of  wood  to  60  tons  of  matte 0.25 

Constructing  heap  and  burning 0.32 

Total $1.07 

Second  Fire. 

Fuel— same  as  before  with  addition  of  chips $0.30 

Turning  heap  and  burning 0.40 

Total $0. 70 

Third  Fire. 

Fuel— same  as  second  fire $0.30 

Removing  finished  heap  0.40 

Transportation  to  furnace  and  expense  of  preparing  the 
raw  matte  still  remaining,  which  results  from  the  fused 
matte 0.45 

Total..  ..$1.15 


Total  cost  of  3  burnings $2.92 

6 


CHAPTER  Y. 

STALL  BOASTING. 

AT  just  what  period  in  the  history  of  the  art  it  became 
customary  to  inclose  the  roast-heap  with  a  little  wall  of  earth  or 
mason-work,  in  order  to  protect  it  against  the  elements,  to  con- 
centrate the  heat,  and  to  render  unnecessary  the  tedious  labor 
of  covering  the  sides  with  fine  ore,  is  unknown,  though  Agri- 
cola's  work  on  metallurgy  shows  that  it  was  no  novelty  in  the 
sixteenth  century.  These  simple  walls  have  since  been  height- 
ened and  sometimes  connected  with  an  arched  roof;  the  area 
that  they  inclose  has  been  paved  and  occasionally  furnished 
with  a  permanent  grate ;  and,  more  important  than  all,  the 
interior  of  the  stall  has  been  connected  by  a  flue  with  a  tall 
chimney,  by  which  the  draught  has  been  improved,  thus  short- 
ening the  process  of  oxidation,  while  the  noxious  fumes  are 
discharged  into  the  atmosphere  at  such  a  height  as  to  render 
them  unobjectionable  in  most  cases. 

A  very  great  variation  exists  in  the  size,  shape,  and  general 
arrangement  of  stalls,  hardly  two  metallurgical  establishments 
building  them  after  the  same  pattern,  though  all  essential  dif- 
ferences may  be  properly  considered  by  dividing  them  into 
two  classes  : 

1.  Open  stalls,  suitable  only  for  ore. 

2.  Covered  stalls,  suitable  for  both  ore  and  matte. 

1.  Open  Stalls. — Any  attempt  at  an  exhaustive  description 
of  the  different  patterns  of  ore-stalls  that  human  ignorance,  as 
well  as  ingenuity,  has  invented,  would  be  a  waste  of  space. 
They  all  consist  of  a  comparatively  small  paved  area,  sur- 
rounded by  at  least  three  permanent  walls,  and  usually  having 
an  open  front,  which  is  loosely  built  up  at  each  operation,  to 
confine  the  contents.  The  back  or  sides,  or  both,  are  pierced 
with  small  openings  communicating  with  a  flue  common  to  a 
large  number  of  stalls  that  enters  a  high  stack.  The  draught 


STALL    ROASTING.  83 

is  confined  to  these  passages  by  covering  the  surface  of  the 
ore  with  a  layer  of  fines.  From  the  great  variety  of  existing 
patterns,  one  built  at  the  works  of  the  Parrot  Copper  and  Sil- 
ver Company,  of  Butte  City,  Montana,  is  selected  for  descrip- 
tion as  possessing  exceptional  advantages  as  regards  cheap- 
ness of  construction,  convenience  of  filling  and  emptying, 
economy  of  fuel,  and  general  adaptability. 

The  stalls  may  be  built  either  of  common  red  brick,  of 
stone,  or,  far  better,  of  slag  molded  into  large  blocks,  which, 
from  their  size  and  weight,  require  little  or  no  extraneous  sup- 
port ;  while  brick  demand  thorough  and  extensive  tying  to- 
gether with  iron-work,  and  stone  of  proper  size  and  shape  is 
expensive  and  is  apt  to  crack  when  exposed  to  great  fluctu- 
ations of  temperature. 

As  these  so-called  "slag-brick"  are  invaluable  for  walls 
and  foundations,  and  in  fact  for  every  purpose  for  which  the 
most  expensive  cut  granite  would  prove  available,  and  as  they 
can  be  produced  from  almost  any  ordinary  copper  slag,  a  brief 
description  of  the  cheapest  and  best  method  of  manufacturing 
them  is  appended. 

MANUFACTURE  OF  SLAG-BRICK. 

These  are  generally  made  from  the  slag  of  reverberatory 
smelting-f  urn  aces,  both  because  this  material  is  usually  more 
siliceous  than  any  other,  and  also  because,  during  the  process 
of  skimming,  it  can  be  obtained  in  large  quantities  in  a  very 
brief  space  of  time.  There  should  be  no  difficulty,  however, 
in  making  the  brick  from  the  slag  of  a  blast-furnace,  provided 
the  smelting  is  sufficiently  rapid  to  fill  the  molds  properly, 
and  that  it  is  not  so  basic  as  to  yield  too  fragile  a  material  on 
cooling.  Even  with  exceedingly  brittle  blocks,  produced  from 
a  highly  ferruginous  ore,  excellent  and  durable  walls  can  be 
constructed,  provided  the  blocks  are  placed  in  position  unin- 
jured ;  for  they  will  bear  an  immense  crushing  weight  with 
impunity,  and  seem  to  defy  the  action  of  the  elements. 

Assuming  the  slag  to  be  obtained  from  a  reverberatory 
furnace,  the  process  of  preparing  the  molds  should  be  begun 
as  soon  as  possible  after  the  slabs  from  the  previous  skimming 
have  been  removed  and  all  chips  and  fragments  cleared  from 


84        MODEKN  AMEEICAN  METHODS   OF  COPPEE  SMELTING. 

the  sand  bed  by  the  aid  of. a  close-toothed  iron  garden-rake. 
Ordinary  loam — or  a  natural  mixture  of  fine  sand  and  clay  of 
such  consistence  that,  when  slightly  moistened,  it  will  ball 
firmly  in  the  hand — is  the  proper  material  for  the  molds, 
which  should  be  formed  by  means  of  a  number  of  wooden 
blocks,  of  the  required  size,  carefully  smoothed  and  slightly 
tapered  to  facilitate  their  removal  from  the  sand,  and  furnished 
with  a  30-inch  handle,  inserted  in  their  upper  surface.  These 
slag  blocks  are  molded  on  the  flat,  in  the  same  manner  as  ordi- 
nary red  brick ;  and  after  leveling  off  the  pile  of  dampened 
sand  to  form  a  smooth  and  horizontal  bed,  the  wooden  blocks 
— some  twelve  in  number  on  each  side  of  the  skimming-door — 
are  arranged  in  a  double  row,  four  inches  apart  between  blocks, 
and  the  same  distance  between  the  two  parallel  rows. 

Besides  the  ordinary  deep  excavation  for  the  plate  slag,  a 
second  bed  should  be  left  on  each  side,  between  the  former 
and  the  first  brick  mold  right  and  left,  both  for  the  purpose  of 
settling  any  grains  of  metal  that  may  be  accidentally  drawn 
over  during  the  process  of  skimming,  and  to  act  as  a  regulat- 
ing reservoir  to  lessen  the  sudden  impulse  of  the  waves  of  slag 
that  follow  each  motion  of  the  rabble,  and  thus  to  prevent  the 
destruction  of  the  very  fragile  sand  molds.  The  entire  bed  is 
constructed  on  an  inclination  of  about  one  half-inch  to  the 
foot ;  the  plate  slag  forming  the  summit,  while  the  double  row 
of  molds  slopes  away  from  it  in  each  direction  laterally.  After 
the  wooden  blocks  have  been  placed  on  this  sloping  bed  in  a 
proper  horizontal  position,  and  exactly  equidistant  from  each 
other,  as  determined  by  a  wooden  gauge,  the  remaining  sand, 
very  slightly  but  equably  dampened,  is  shoveled  back  again, 
and  carefully  trodden  and  tamped  evenly  into  all  the  inter- 
spaces and  around  the  outside  edges  of  the  blocks,  until  it 
reaches  the  level  of  their  upper  surface.  This  is  a  very  brief 
operation ;  for  it  is  not  essential  to  tamp  the  sand  very  firmly 
so  long  as  about  an  equal  degree  of  solidity  is  imparted  to  all 
portions  of  it.  A  cylinder  of  hard  wood — three  inches  in 
diameter  and  four  inches  long — which,  when  placed  length- 
wise, fits  exactly  between  each  two  molds,  is  laid  upon  its  side, 
and,  by  a  few  blows  of  the  mallet,  driven  into  the  sand,  thus 
when  removed  forming  a  little  gutter  through  the  middle  of 


STALL   ROASTING.  85 

the  partition  wall,  and  connecting  each  pair  of  adjacent  cavi- 
ties in  such  a  manner  that  the  flow  of  slag  through  either 
entire  lateral  system  meets  with  no  impediment.  The  wooden 
blocks  are  then  removed  from  their  sand  bed  with  the  greatest 
care,  it  often  being  necessary  to  loosen  them  by  gentle  tapping 
and  other  means  familiar  to  the  experienced  molder.  The  bed 
requires  only  a  few  hours'  drying  to  fit  it  for  the  slag. 

By  the  time  the  charge  is  ready  for  skimming,  say  in  three 
hours  or  less  after  the  completion  of  the  bed  just  described,  it 
should  be  in  proper  condition,  and  the  furnace  helper,  armed 
with  a  small  rabble-shaped  hoe,  stands  beside  the  skimmer 
ready  to  turn  the  stream  of  slag  into  the  proper  molds,  remove 
obstructions  from  the  gutters,  break  through  the  rapidly  form- 
ing crust  if  indications  of  chilling  appear  on  the  surface  of 
the  molten  bath,  and  see  in  general  that  the  process  of  filling 
the  molds  proceeds  in  a  proper  manner.  As  soon  as  this 
operation  is  concluded,  a  few  shovelfuls  of  sand  should  be 
thrown  over  the  surface  of  the  slabs  to  prevent  sudden  and 
unequal  chilling.  By  the  time  the  new  charge  is  in  the  fur- 
nace and  the  assistant  is  at  liberty  to  attend  to  his  bricKs,  they 
will  usually  be  found  ready  for  removal,  though  still  at  a  red 
heat  on  the  surface  and  in  most  cases  quite  liquid  in  the  inte- 
rior. It  is  essential  that  they  be  removed,  and  the  slight 
roughnesses  that  arise  from  the  broken  ends  corresponding  to 
the  gutters  through  which  they  were  filled  be  trimmed  off  with 
a  small  cutting  hammer  while  they  are  still  quite  hot,  as  it  is 
just  at  this  stage  that  they  possess  the  highest  degree  of  tough- 
ness, and  permit  of  manipulations  that,  if  they  were  cool,  would 
inevitably  break  them  into  fragments.  These  slabs  are  best 
removed  from  the  furnace  by  being  loaded  upon  the  low  iron 
barrow  commonly  used  for  the  transportation  of  pigs  of  slag 
and  matte.  The  loading  is  effected  by  means  of  a  long  five- 
eighths  inch  iron  rod,  bent  into  a  hook  at  one  end,  and  the 
blocks  are  then  wheeled  out  upon  the  dump,  where  a  special 
workman  trims  them  properly,  rejecting  all  that  are  imperfect 
or  already  cracked,  and  when  cool,  piles  them  into  rows  to 
remain  until  needed.  The  most  useful  size  for  general  pur- 
poses has  been  found  to  be  about  8  by  10  by  20  inches,  and 
weighing  about  85  pounds ;  but  by  simply  changing  the  form 


86        MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 


of  the  pattern,  they  may  be  produced  of  any  desired  shape  or 
size,  although  experience  has  shown  that  it  is  not  economy  to 
attempt  the  manufacture  of  very  thin  slabs,  or  of  any  weight 
below  45  pounds.  The  immense  value  of  this  building  mate- 
rial, produced  from  an  otherwise  worthless  material,  and  ob- 
tainable in  rectangular  shape  for  plain  walls  and  foundations, 
in  wedge  shape  for  arches  and  for  forming  a  circle  in  walling 
wells  and  for  many  other  daily  needs,  can  be  fully  appreciated 
only  by  those  who  have  had  occasion  to  build  in  a  country 
where  rock  was  unobtainable  and  brick  poor  and  expensive. 

A  particular  distinction  should  be  made  between  the  old 
plan  of  making  slabs  of  slag  in  iron  molds,  as  practiced  all 
over  the  world,  and  this  method  of  sand  molding,  for  which 

ROAST  STALLS  FOR  ORE. 

CHIMNEY 


CROSS  SECTION  THROUGH  A.B. 
SCALED  IN.  =  1  FOOT 


TRACK  TO 
SMELTER 


A- 


I      .      I  PIP 


I.  I   ,  <L_L 


I   ,   I 


I   .  I 


1,1,1 


J L 


a.a.— Draught  holes  connecting 
with  Flue  in  sidewalls. 
b.b.—Flue  holes  into  Main 
Culvert. 


-ro-nS- 


iii 


I.I,   IPII 


TRACK  TO 
SMELTER 
J » 


>j 


the  profession  is  indebted  to  Mr.  J.  E.  Gaylord,  Secretary  of 
the  Parrot  Silver  and  Copper  Company.  The  author  is  well 
aware  that  molding  in  sand  has  been  practiced  also,  but  never, 
so  far  as  he  knows,  with  such  results  as  are  obtained  by  the 
method  indicated. 

To  return  to  the  roasting  stalls.  Assuming  that  they  are 
to  be  built  of  the  material  just  described,  and  without  any  iron- 
work for  anchoring,  and  that  each  stall  is  to  burn  a  charge  of 
20  tons  and  be  again  cleared  out  in  10  days,  thus  furnishing  2 
tons  a  day,  it  will  require  some  56  stalls  to  furnish  100  tons  of 
ore  a  day,  allowing  some  12  per  cent,  in  excess  of  the  needful 


STALL  ROASTING. 


87 


capacity  to  permit  of  repairs.  The  weight  of  ore  as  brought 
to  the  stalls,  and  not  as  taken  from  them,  is  counted  :  its  loss 
during  the  process  of  calcination  depends  upon  the  quality  and 


amount  of  sulphides  present,  and  frequently  reaches  15  per 
cent.,  though  a  considerable  portion  of  the  loss  in  weight  due 
to  the  elimination  of  the  sulphur  is  offset  by  the  gain  in  oxygen. 


88        MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

Such  a  battery  of  stalls  should  always  be  built  in  a  double 
row,  back  to  back,  each  lateral  wall  serving  as  the  division 
between  the  two  adjacent  partitions,  while  the  unbroken  rear 
walls  form  the  sides  of  the  main  flue,  a  space  of  at  least  2  feet 
being  left  between  them,  which  simply  requires  a  4-inch  brick 
arcn  to  form  the  main  flue  for  the  entire  system.  This  also 
constitutes  a  foundation  on  which,  after  a  little  leveling  np  with 
earth,  to  prevent  the  sleepers  from  being  affected  by  the  heated 
masonry  below,  the  narrow  railroad  is  laid  on  which  the  ore 
for  roasting  is  brought  to  any  part  of  a  given  stall  by  means  of 
the  turn-plate  and  movable  rails,  explained  in  the  chapter  on 
Heap  Roasting.  A  double  row  of  28  stalls  (56  in  all)  should 
have  a  flue  at  least  2  by  4  feet  for  the  third  of  the  number 
nearest  the  chimney,  which  may  be  reduced  to  2  by  3  feet  for 
the  middle,  and  2  by  2J  feet  for  the  end  third,  if  any  saving 
can  be  effected  thereby.  The  two  long  rear  walls,  inclosing 
the  main  flue,  should  be  32  inches  thick — once  and  a  half  the 
length  of  a  slag  brick — with  proper  allowance  for  mortar  and 
irregularities,  and  should  be  laid  solely  in  clay  mortar,  which 
designation  throughout  this  entire  work  may  be  understood  to 
mean  merely  common  sticky  mud,  such  as  is  employed  for 
making  a  poor  quality  of  red  brick.  If  ordinary  clay  be  acces- 
sible, it  may  be  mixed  with  sand  in  such  proportions  as  to  slip 
easily  from  the  trowel ;  otherwise,  any  ordinary  sticky  mud 
may  be  used  and  will  be  found  to  form  perfectly  satisfactory 
material  for  laying  all  mason  work  that  is  to  be  exposed  to 
sulphur  fumes  and  a  heat  not  exceeding  a  dull  red. 

The  fact  that  lime  mortar  is  totally  unadapted  to  ordinary 
metallurgical  uses,  although  doubtless  universally  known,  is  for 
some  unaccountable  reason  frequently  not  acted  upon,  and  the 
result  in  most  cases  is  the  rapid  and  total  destruction  of  the 
furnace-arch,  chimney,  flue,  or  whatever  structure  may  happen 
to  have  been  put  together  with  such  unfit  material.  The  acid 
vapors  immediately  form  a  sulphate  with  the  lime  present  in 
the  mortar,  and  this,  absorbing  water,  becomes  gypsum  and 
crystallizes,  expanding  with  great  force,  breaking  the  joints, 
and  soon  crumbles  and  washes  away.  It  is  quite  proper  to  use 
lime  mortar  in  such  portions  of  the  structure  as  are  free  from 
contact  with  sulphurous  gases,  and  yet  require  unusual  strength, 


STALL  ROASTING.  89 

which  cannot  be  obtained  with  the  clay  substitute.  Such,  for 
instance,  as  in  the  construction  of  chimneys  for  metallurgical 
purposes,  where  the  best  results  can  only  be  obtained  by  the 
employment  of  both  of  these  substances ;  lime  mortar  for  the 
outside  work,  while  the  common  clay  mud  is  merely  used  for 
the  inside  layer,  and  the  joints  thoroughly  protected  against 
any  invasion  of  the  sulphur  gases  by  plastering  the  whole  in- 
terior with  a  thin  coating  of  clay  mortar,  tempered  with  sand 
to  such  an  extent  that  it  will  not  crack  and  fall  off  in  sheets. 
Further  reference  will  be  made  to  this  point  in  the  chapter  on 
Furnace  Building.  The  constant  and  flagrant  violation  of  this 
law  is  a  sufficient  reason  for  its  frequent  reiteration.  A  recent 
example  suggests  itself,  where  the  arches  of  a  number  of  very- 
expensive  and  nearly  new  calcining-furnaces  had  fallen  in, 
causing  a  very  heavy  loss.  A  conversation  with  the  mason 
who  built  them  brought  out  the  fact  that  they  were  constructed 
with  lime  mortar,  he  having  had  no  orders  to  the  contrary. 

The  size  of  the  stall  is  somewhat  dependent  upon  the  quality 
of  the  ore  to  be  roasted,  a  highly  siliceous  ore  with  a  compara- 
tively low  percentage  of  sulphur  permitting  a  much  wider  and 
higher  stall  than  an  ore  with  little  gangue,  and  especially  than 
one  containing  a  considerable  portion  of  iron  pyrites,  in  which 
case,  extensive  and  unavoidable  sintering  will  follow  any  at- 
tempt at  increasing  the  size  of  the  stall.  A  safe  size  for  an 
average  ore,  containing  a  moderate  amount  of  pyrite  and  de- 
manding careful  handling,  is  8  feet  in  length  by  6  feet  in  height 
by  6£  feet  in  width,  the  latter  measurement  being  the  maxi- 
mum that  is  safe  under  any  ordinary  circumstances.  It  is 
best  to  build  the  lateral  walls  of  the  same  thickness  as  the 
rear  division,  the  increased  stability  and  durability  of  the 
entire  structure  well  repaying  the  slight  additional  expense  in 
labor  and  material.  The  bottom  should  be  paved  with  the 
same  slabs  placed  flatwise  and  exactly  reversed  from  the  posi- 
tion in  which  they  lay  when  formed ;  their  upper  surface  now 
going  downward,  while  their  original  lower  surface,  which 
should  be  perfectly  smooth  and  level,  now  comes  upward. 
The  connection  with  the  main  flue  is  effected  by  means  of  8 
or  10  small  rectangular  openings — 2  by  6  inches — in  the  rear 
wall,  in  two  or  more  rows,  and  at  a  considerable  distance  from 


90        MODERN  AMERICAN   METHODS   OF   COPPER  SMELTING. 

the  ground.  These  are  kept  tightly  closed  by  means  of  a 
bunch  of  old  rags  or  a  ball  of  clay,  when  there  is  no  occasion 
for  their  remaining  open ;  otherwise,  the  draught  of  the  entire 
system  might  suffer. 

The  only  air  admitted  to  these  stalls  originally,  at  the  Par- 
rot works,  came  through  such  interstices  as  were  left  in  roughly 
building  up  the  temporary  front  wall ;  but  experiments  led  to 
the  addition  of  some  4  or  6  similar  openings  in  each  lateral 
wall,  which  did  not  communicate  with  the  main  culvert,  but 
connected  with  the  outside  air  by  means  of  a  small  flue  run- 
ning longitudinally  through  each  division  wall,  though  not 
extending  so  far  as  the  central  passage.  This  innovation  has 
been  followed  by  a  decided  improvement  in  the  oxidation  of 
the  ore  and  a  great  diminution  in  the  amount  of  matte  pro- 
duced. An  essential  precaution  in  the  management  of  these 
stalls  is  to  maintain  a  thick  coat  of  clay  plastering  over  their 
entire  interior  surface,  by  which  the  heated  ore  is  kept  from 
sticking  to  the  walls  and  causing  the  rapid  destruction  of  the 
mason-work.  A  few  moments'  attention  to  the  empty  struc- 
ture after  each  operation  will  keep  the  plastering  intact  and 
greatly  lessen  the  cost  of  repairs.  As  the  entire  success  of 
this  process  depends  upon  the  strength  and  regularity  of  the 
draught,  a  stack  of  considerable  size  and  height  is  essential. 

A  battery  of  56  stalls  as  described  requires  at  sea  level  a 
chimney  75  feet  high,  and  with  an  internal  area  of  at  least  9 
square  feet,  as  will  be  further  explained  in  the  chapter  on  the 
construction  of  calcining-furnaces.  Any  economy  in  the  direc- 
tion of  diminishing  the  size  of  this  important  adjunct  will  be 
immediately  noticed  in  the  lengthening  of  the  roasting  pro- 
cess, and  may  reduce  the  capacity  of  the  stalls  to  an  incredible 
degree.  The  draught  is  regulated  by  means  of  a  sheet-iron 
damper  hung  in  the  main  flue,  close  to  its  junction  with  the 
chimney,  while  the  same  office  is  accomplished  for  individual 
stalls  by  partially  filling  the  draught-holes  in  the  rear  wall  with 
bits  of  bricks  or  balls  of  clay.  In  no  portion  of  the  process, 
are  the  skill  and  care  of  the  roasting  foreman  better  displayed 
than  in  his  management  of  the  draught,  which  must  be  varied 
according  to  the  season,  and  temperature  of  the  air,  as  well  as 
with  the  changing  character  of  the  ore. 


STALL  EOASTING.  91 

As  already  intimated,  a  stall  of  the  size  and  pattern  just 
described  will  hold  about  twenty  tons  of  pyritous  ore,  which 
should  be  kindled  with  the  very  smallest  possible  quantity  of 
wood  that  will  set  it  thoroughly  on  fire.  This  is  essential  for 
a  far  more  important  reason  than  the  mere  saving  in  fuel ;  for 
the  slightest  increase  in  the  contents  of  the  bed  of  wood  on 
which  the  rock  is  heaped  will,  with  pyritous  or  otherwise  easily 
fusible  ores,  cause  an  amount  of  sintering  and  a  formation  of 
matte  entirely  disproportionate  to  the  cause.  Repeated  trials 
can  alone  determine  the  various  minutiae  of  this  description 
essential  to  the  best  possible  results  with  the  material  under 
treatment ;  but,  in  most  cases,  where  the  ore  is  at  all  pyritous, 
good  sound  wood  will  be  found  to  produce  too  fierce  a  heat 
for  the  purpose,  and  recourse  must  be  had  to  decayed  wood, 
which  can  usually  be  obtained  at  from  one-half  to  two-thirds 
of  the  price  of  the  sound  fuel.  For  an  ore  containing  30  per 
cent,  sulphur  and  say  25  per  cent,  silica,  25  cubic  feet  of  rot- 
ten wood,  or  about  one-fifth  of  a  cord,  will  be  found  ample ; 
but  this  small  proportion  of  fuel — only  one  one-hundredth  of 
a  cord  to  the  ton — must  be  utilized  in  a  proper  manner,  and 
with  the  most  rigid  economy  and  exactitude,  or  the  heap  will 
miss  fire  completely,  doubling  the  cost  of  the  operation,  as  well 
as  interfering  with  the  estimated  production  of  the  plant.  A 
quarter  of  an  hour  spent  in  watching  the  manipulations  of  an 
experienced  roaster  is  better  than  pages  of  description,  though 
the  operation  of  preparing  a  stall  for  its  ore  charge  is  far  from 
complicated. 

After  seeing  that  the  layer  of  clay  on  the  inclosing  walls  is 
renewed  with  the  plastering-trowel  where  necessary,  and  that 
the  draught-holes  are  open  to  the  extent  dictated  by  former 
experience,  a  central  longitudinal  and  two  lateral  flues  are  con- 
structed on  the  floor  of  the  stall  out  of  large,  irregular  frag- 
ments of  ore.  These  are  merely  to  introduce  air  to  the  inte- 
rior and  to  insure  the  rapid  and  thorough  kindling  of  the  entire 
structure.  They  are  filled  and  surrounded  with  dry  kindling- 
wood,  and  the  greater  part  of  the  fuel,  split  into  long,  thin 
sticks  from  the  large  rotten  logs  and  poles  that  are  usually  pro- 
vided, is  disposed  in  a  thin  layer  over  the  bottom  of  the  stall, 
the  amount  slightly  increasing  toward  each  side.  The  structure 


92        MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

is  now  filled  with  coarse  ore,  and  the  ragging  distributed 
throughout  the  entire  contents  rather  than  concentrated  in  a 
considerable  layer  merely  upon  the  surface.  As  the  stall  be- 
comes gradually  filled,  single  small  sticks  of  wood  are  placed 
between  the  ore  and  the  lateral  and  back  walls  ;  while  between 
the  contents  of  the  stall  and  the  front  wall,  which  is  built  up 
with  large  lumps  of  ore  or  stall  matte,  a  considerable  quantity 
of  light  wood  is  introduced  to  insure  the  thorough  desulphuri- 
zation  of  the  anterior  surface.  A  single  car-load  of  ragging  is 
spread  on  top  of  the  coarse  ore,  and  upon  this  a  three-inch 
layer  of  shavings,  bark,  and  chips  is  placed  as  a  bed  for  about 
one  and  a  half  tons  of  raw  fines,  which,  if  disposed  in  the  ex- 
act manner  indicated,  and  covered  thoroughly  with  well-roasted 
ore  from  a  contiguous  stall,  will  be  thoroughly  desulphurized, 
and  the  covering  layer  itself  being  in  a  well  calcined  condition, 
the  entire  contents,  after  burning,  may  be  passed  on  to,  the 
next  operation. 

It  is  only  by  employing  great  care,  and  after  repeated 
trials,  that  the  requisite  skill  will  be  attained  to  thoroughly 
calcine  the  large  proportion  of  fines  just  indicated ;  but  when 
one  reflects  that  it  amounts  to  some  seven  per  cent,  of  the  en- 
tire ore,  and  perhaps  one-half  of  the  total  fines  produced,  it 
will  be  seen  that  the  result  is  worthy  of  any  pains  that  can  be 
expended  on  it.  The  large  pieces  of  raw  ore  that  are  em- 
ployed in  building  the  flues  and  front  wall  become  gradually 
oxidized  upon  the  surface,  and  slowly  crumble  away  and  mix 
with  the  finished  product  until  they  totally  disappear  and  are 
replaced  by  fresh  pieces.  When  the  ore  is  to  be  removed,  the 
front  wall  is  taken  down,  and  the  lumps  of  ore  from  it  are  piled 
out  of  the  way,  to  be  again  used  for  the  same  purpose. 

The  stall  should  be  fired  at  night,  as  the  smoke  is  so  dense 
during  the  first  few  hours,  and  the  draught  so  sluggish,  that 
only  a  small  part  of  the  fumes  find  their  way  into  the  proper 
channel ;  but  by  the  time  the  wood  is  consumed,  the  entire 
structure  has  become  so  much  warmer  as  greatly  to  improve 
the  draught.  The  sulphur  and  other  products  of  volatilization 
and  "  sweating  " — alluded  to  in  describing  the  management  of 
roast-heaps — form  a  sort  of  crust  upon  the  surface,  and  seal 
all  interstices  connecting  with  the  atmosphere,  and  force  nearly 


STALL  ROASTING.  93 

all  fumes  to  pass  into  the  flue,  thus  greatly  abating  a  nuisance. 
For  the  first  twenty-four  hours,  the  fire  is  confined  to  those 
portions  of  the  ore  that  were  in  immediate  contact  with  the 
fuel.  The  process  of  oxidation  advances  very  rapidly,  and  by 
the  close  of  the  second  day  it  is  hardly  possible  to  bear  the 
hand  upon  the  middle  of  the  upper  surface  of  the  stall,  show- 
ing that  at  least  one-half  the  contents  is  already  in  combustion. 
By  the  end  of  the  fourth  day  a  similar  degree  of  temperature 
may  be  felt  upon  the  upper  surface,  at  the  very  back  of  the 
stall,  proving  that  the  process  has  by  that  time  invaded  the 
entire  length  and  breadth  of  the  stall,  though  considerable 
time  is  still  necessary  for  its  thorough  completion. 

The  successful  progress  of  the  process  is  clearly  marked  by 
the  great  rise  in  height  of  the  entire  contents,  gaining  some 
three  inches  in  a  single  day,  and  frequently  ascending  some  12 
inches  above  the  level  of  the  walls,  at  which  it  stood  at  the  be- 
ginning of  the  operation,  aside  from  the  free  space  left  to  be 
filled  out  with  ore  from  the  disappearance  of  the  fuel,  amount- 
ing to  some  25  cubic  feet.  This  striking  phenomenon,  unfa- 
miliar to  those  accustomed  only  to  heap  roasting,  where  a  set- 
tling rather  than  a  rising  of  the  entire  mass  occurs,  is  simply 
due  to  the  fact  that,  in  all  cases  of  oxidizing  roasting,  a  greater 
or  less,  though  always  very  marked,  increase  in  bulk  occurs 
from  the  swelling  and  fissuring  of  the  oxidized  ore.  The  con- 
tents of  the  roast-heap,  being  perfectly  free  and  unconfined,  sim- 
ply spread  out  laterally,  while  the  consumption  of  the  thick 
bed  of  fuel  on  which  it  rests  detracts  considerably  from  its 
height.  The  walls  of  the  stall,  however,  inclose  the  ore  in  a 
rigid  grasp,  making  it  absolutely  necessary  that  any  increase 
in  bulk,  beyond  that  very  slight  amount  necessary  to  replace 
the  space  occupied  by  the  fuel,  should  take  place  vertically. 
In  a  badly  burned  stall,  where  extensive  sintering  has  taken 
place,  a  sufficient  amount  of  the  sulphides  has  melted  into  a 
solid  mass  to  cause  a  decided  diminution  in  bulk  instead  of  an 
increase,  and  the  occurrence  of  crater-like  depressions  in  the 
surface  of  the  ore  is  positive  evidence  of  such  local  fusions. 
That  the  pressure  resulting  from  the  increase  in  bulk  is  some- 
thing quite  tangible,  may  be  inferred  from  the  frequent  push- 
ing outward,  or  even  overturning  of  the  heavy  lateral  walls  of 


94       MODEKN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

a  stall,  provided  one  or  the  other  of  its  contiguous  compart- 
ments are  either  empty  or  unbraced,  while  the  temporary  front 
wall  would  inevitably  be  thrown  down  within  the  first  day 
after  kindling  if  not  strongly  supported  by  timbers. 

The  length  of  time  necessary  for  the  process  under  consid- 
eration is  another  uncertain  factor.  If  the  stall  be  left  undis- 
turbed, it  will  usually  burn  quietly  for  a  period  of  twelve  days, 
demanding  little  or  no  attention  beyond  an  occasional  shovel- 
ful of  covering  if  heating  too  fiercely  at  any  one  point,  and 
requiring  about  three  days  additional  to  cool  sufficiently  to 
remove  with  comfort ;  but,  under  ordinary  every  day  circum- 
stances, no  such  moderation  can  be  practiced,  and  the  period 
of  each  operation  can  be  curtailed,  without  any  especial  dam- 
age, to  one-half  this  time.  To  accomplish  this  without  detri- 
ment to  the  process  of  desulphurization,  the  following  precau- 
tions must  be  adopted  :  As  soon  as  the  anterior  surface  of  the 
ore  is  so  cool  as  to  impart  no  disagreeable  sensation  to  the 
hand,  the  temporary  front  wall  should  be  removed,  the  natural 
adhesion  common  to  all  sulphureted  ores  when  roasted  in 
lumps  preventing  the  caving  of  the  vertical  ore  face,  which 
should  be  most  carefully  attacked  with  pick  and  shovel,  every 
precaution  being  taken  not  to  penetrate  beyond  the  line  of 
comparative  cooling,  and  only  so  much  ore  being  removed  at 
any  one  operation  as  is  consistent  with  the  uninterrupted  prog- 
ress of  the  roasting  in  the  mass  behind.  At  least  six  or  eight 
inches  of  ore  should  be  left  between  the  outer  air  and  the  line 
of  fire,  and  any  sudden  elevation  of  the  surface  temperature^ 
as  well  as  increased  difficulty  in  detaching  the  ore  from  the 
face  on  which  work  is  prosecuted,  are  signs  to  stop.  To  illus- 
trate the  ease  with  which  the  contents  of  a  well-burned  stall 
can  be  handled,  the  entire  charge  of  ore  from  such  a  stall  can 
be  removed  with  nothing  stronger  than  a  shingle. 

The  first  car-load  is  usually  taken  from  the  stall  at  the  close 
of  the  fourth  day,  and  the  amount  capable  of  removal  may  be 
rapidly  increased,  until  in  seven  days  more  the  compartment  is 
again  empty. 

By  this  careful  method  of  constant  and  systematic  slicing, 
some  two  or  three  tons  of  well-burned  ore  may  be  taken  daily 
from  each  of  40  or  50  stalls,  and  the  capacity  of  the  roasting 


STALL   BOASTING.  95 

plant  rendered  more  than  double  what  it  would  be  if  they  were 
left  untouched  for  the  time  necessary  for  their  complete  desul- 
phurization  and  cooling ;  while  the  process  of  oxidation  does 
not  suffer  in  the  slightest  degree  if  the  precautions  just  enu- 
merated are  adhered  to. 

In  the  case  of  ores  containing  arsenical  pyrites,  or,  indeed, 
in  the  presence  of  any  form  of  arsenical  or  antimonial  combi- 
nations, a  considerable  proportion  of  the  same  that  would 
otherwise  go  into  the  next  operation  in  the  shape  of  anti- 
monates  and  arsenates  may  be  volatilized  and  completely  dis- 
persed by  the  admixture  of  chips,  small  coal,  brush-wood  or 
other  carbonaceous  materials,  which,  as  in  heap  roasting,  exer- 
cise a  powerful  reducing  influence  upon  the  products  of  oxida- 
tion just  mentioned,  and  volatilize  them  in  a  metallic  form. 
This  simple  precaution  is  of  much  greater  value  in  the  calcina- 
tion of  similar  compounds  in  a  pulverized  condition  in  fur- 
naces, where  the  different  periods  of  oxidation  and  reduction 
are  under  the  control  of  the  operator,  and  can  be  made  to  fol- 
low each  other  in  the  manner  most  conducive  to  the  object  in 
view  ;  but  even  in  the  rude  process  under  consideration,  expe- 
rience has  shown,  in  many  cases,  that  a  decided  improvement 
in  the  grade  of  copper  has  resulted  from  this  device,  the  sim- 
plicity and  economy  of  which  are  among  its  strongest  recom- 
mendations. 

The  results  obtained  in  stall  roasting  vary  little  as  com- 
pared with  those  from  burning  in  heaps.  On  the  whole,  it  is 
not  quite  so  easy  to  prevent  the  formation  of  matte  in  the  for- 
mer practice,  nor  do  average  and  oft-repeated  examinations 
show  quite  as  good  results  in  the  elimination  of  the  sulphur. 

As  circumstances  may  arise  where  it  becomes  the  duty  of 
the  constructing  metallurgist  to  decide  between  these  two  sys- 
tems, to  the  positive  exclusion  of  all  methods  involving  the  pul- 
verization of  the  ore,  and  to  give  his  reasons  for  and  against  each 
method,  that  his  employers  may  also  have  some  idea  of  the 
matter  on  which  to  base  their  advice  or  to  rest  the  confirma- 
tion of  his  decision,  it  will  be  well  concisely  to  review  the  com- 
parative advantages  and  drawbacks  of  heap  and  stall  roasting.* 

*  See  article  on  "  The  Mines  and  Smelting- Works  of  Butte  City,"  by  the 
author,  in  the  United  States  publication  on  Mineral  Resources  (by  A.  Wil- 


96       MODERN   AMERICAN  METHODS   OF   COPPER  SMELTING. 

The  first  and  most  obvious  advantage  of  the  system  of  heap 
roasting  is  the  apparent  cheapness  and  simplicity  of  the  plant, 
only  a  level  area  being  required,  without  furnaces,  flues,  stacks, 
or  other  expensive  appurtenances. 

The  extreme  simplicity  of  the  method  and  the  very  satis- 
factory results  obtained  under  proper  management  also  speak 
in  its  favor ;  but  further  than  this,  no  arguments  can  be  ad- 
vanced in  support  of  the  process. 

Even  the  economy  in  first  cost  of  plant  will  be  found  more 
apparent  than  real,  when  the  expense  of  the  trestle-work  and 
track,  as  well  as  the  establishment  of  the  different  grades  be- 
tween spalling-shed,  roast-yard,  and  smelting-house  levels  are 
considered,  and  no  one  will  deny  the  absolute  necessity  for 
such  an  arrangement  if  work  on  a  large  scale  is  to  be  prose- 
cuted with  any  degree  of  economy. 

A  careful  comparative  calculation  of  costs,  corrected  by  the 
results  of  actual  work,  shows  that  under  ordinary  circum- 
stances the  difference  -in  cost  between  the  two  plants  under 
consideration  is  too  trifling  to  have  much  weight  in  the  choice 
of  methods,  and  may  even  be  on  the  side  of  the  stalls  in  cases 
where  the  natural  conformation  of  the  land  is  unfavorable  for 
the  establishment  of  the  terraces  necessary  for  cheap  heap 
roasting. 

A  far  more  important  reason  for  the  adoption  of  the  stall 
system  is  the  great  saving  in  time,  by  which  the  delay  in- 
cidental to  the  cruder  process  of  calcination  is  diminished  by 
at  least  eighty  per  cent. 

In  works  of  large  capacity,  this  becomes  a  question  of  vital 
importance  ;  for  few  smelting  companies  are  so  amply  provided 
with  capital  as  to  carry  a  constant  stock  of  some  ten  thousand 
tons  of  ore,  representing  a  money  value  of  several  hundred 
thousand  dollars,  which  is  not  at  all  an  extravagant  estimate 
for  works  of  the  capacity  under  consideration.  The  circum- 
stance that  this  amount  may  be  reduced  to  a  sum  not  exceed- 
ing one-fifth  of  the  above  by  the  substitution  of  the  quicker 
method  of  calcination  is  a  weighty  argument  for  its  adoption. 

liams,  Jr. ,  1885).  The  third  method  of  roasting  lump  ore — that  is,  in  con- 
tinuous kilns — is  only  suited  to  certain  peculiar  conditions,  and  need  not  be 
considered  when  comparing  the  other  two  systems. 


STALL  BOASTING.  97 

By  a  careful  comparison  of  the  expense  of  the  two  opera- 
tions, we  have  already  seen  that  a  saving  of  about  one- third 
may  be  effected  by  the  use  of  stalls,  owing  principally  to  their 
greater  economy  in  fuel  and  labor. 

A  still  further  advantage  may  be  claimed  for  them  in  the 
concentration  of  all  noxious  fumes  into  a  single  flue,  and  their 
discharge  into  the  atmosphere  at  such  an  elevation  as  to  in- 
sure their  gradual  diffusion  and  dispersion  without  annoyance 
or  damage.  This  is  a  great  boon  to  the  surrounding  country, 
and  more  especially  to  the  workmen  employed  in  the  process 
of  roasting,  as  any  one  familiar  with  the  atmosphere  of  an 
establishment  where  heap  roasting  is  practiced  can  testify. 

Still  further  may  be  mentioned  the  considerable  saving 
effected  by  the  thorough  roasting  of  the  entire  contents  of  the 
stall,  including  even  the  fine  covering  material,  all  of  which  is 
in  condition  for  the  succeeding  operation ;  whereas,  in  the 
case  of  heap  roasting,  at  least  10  per  cent,  of  the  entire  stock 
requires  a  second  handling.  Here  may  also  be  considered  the 
serious  losses  of  metal  from  wind,  rain,  and  other  atmospheric 
causes,  which,  although  not  entirely  obviated  by  the  employ- 
ment of  stalls,  are  at  least  greatly  lessened ;  the  saving  in  a 
certain  plant  of  moderate  capacity,  amounting  in  a  single  year, 
according  to  the  author's  calculations,  to  more  than  sufficient 
to  cover  the  entire  cost  of  erecting  the  stalls. 

But  the  most  important  advantage  possessed  by  stall  roast- 
ing over  heap  roasting  in  an  ordinarily  moist  climate — if  the 
process  be  carried  on  in  the  open — is  the  prevention  of  loss  by 
leaching. 

We  have  already  pointed  out  the  necessity  of  guarding 
against  this  loss  by  every  possible  means  at  our  disposal ;  but 
even  with  every  care  a  considerable  loss  from  this  source  can- 
not be  avoided  in  any  ordinary  climate. 

Mr.  Wendt*  gives  some  important  figures  bearing  on  this 
point,  relating  to  heap  roasting  as  formerly  practiced  at  Duck- 
town,  Tenn.,  where,  however,  the  rain-fall  is  exceptionally  great. 
"We  quote  also  his  estimates  of  cost,  which,  taking  into  account 
the  low  cost  of  fuel  and  labor,  correspond  closely  with  our  own. 

*  See  The  Pyrites  Deposits  of  the  Alleghanies,  by  A.  F.  Wendt.     New 
York,  1866,  page  19. 

7 


MODEEN  AMERICAN  METHODS   OF  COPPER  SMELTING. 


"  Ore-roasting,  as  thus  carried  out  (in  heaps),  was  a  very 
economical  process  in  point  of  labor  and  fuel.  On  an  average, 
one  cord  of  wood  was  consumed  for  40  net  tons  of  ore  for 
each  fire.  The  cost  of  labor  in  the  first  fire  was  5  cents  per 
1000  pounds  for  both  Mary  and  East  Tennessee  ores  ;  for  the 
second  fire,  7  cents  and  6  cents  respectively  were  paid ;  and 
for  fine  ores,  the  pay  was  12  cents  per  M. 

"  The  exact  cost  per  net  ton  of  ore  was  as  follows  : 

A,  cord  wood,  at  $3 $0.15 

Labor,  1st  fire 10 

Labor,  2d  fire 14 

Materials 03 

Total  per  ton $0.42 

"  The  losses  of  copper  in  the  above-described  roasting  have 
been  very  generally  ignored  in  judging  of  its  expense.  At 
least,  proper  emphasis  has  never  been  laid  on  them. 

"  Owing  to  an  unexplained  difference  of  several  hundred 
thousand  pounds  between  the  fine  copper  produced  at  the 
Ducktown  smelter  during  a  period  extending  over  several 
years,  and  the  monthly  fine  copper  statements  arrived  at  by 
deducting  one  and  one -quarter  unit  from  the  assay  value  of 
the  ores  produced,  the  writer's  attention  was  forcibly  called  to 
this  subject.  A  careful  series  of  experiments  was  instituted ; 
the  results  were  rather  startling.  Repeated  analysis  of  ore 
weighed  into  a  roast-pile,  and  analysis  and  weighing  of  this 
same  ore  when  sent  to  the  matte  furnaces,  proved  an  almost 
incredible  loss. 

"  From  the  large  number  of  experiments  and  analyses,  I 
quote  the  following  striking  examples  : 

Pile  No.  349. — Mary  Ore. 


Gross  weight  of  ore. 

Per  cent,  water. 

Per  cent,  copper. 

Fine  copper,  pounds 

399,213 
204,444 
95,182 
8,663 
34,165 

2-5 
2-0 
3-8 
3-0 
6-0 

5-0 
5-8 
5-0 
5-1 

4-0 

19,461 
11,620 
3,617 
4'28 
1,284 

741,667  pounds  raw  ore  contained  36,410  pounds  copper. 


STALL  ROASTING. 


"The  pile  after  roasting  weighed  741,716  pounds — assayed 
3 '31  per  cent  copper — equivalent  to  24,985  pounds  fine  copper: 
11,125  pounds  copper,  or  31'4  per  cent,  of  the  contents  of  the 
pile,  had  been  lost  while  roasting :  170  days  were  consumed 
in  roasting  the  ore,  and  69  days  in  removing  it  to  thesmelting- 
furnaces.  Hence,  the  ore  lay  exposed  to  the  weather  for  239 
days,  that  is,  eight  months. 

Pile  No.  447. — Mary  Ore. 


Gross  weight  of  ore. 

Per  cent,  water. 

Per  cent,  copper. 

Fine  copper,  pounds 

172,883 
1,532 
198,800 
32,178 
26,865 
32,245 

3-0 
5-5 
2'0 
4'0 
5-5 
3-0 

4.7 
6-3 
4-5 
5-3 
4.6 
6.2 

7,881 
91 
8,767 
1,687 
1,167 
1,939 

464,505  gro.-s  pounds  ore  contained  21,482  pounds  copper. 

"  Weight  of  the  roasted  ore  was  495,566  pounds,  assaying 
2*85  per  cent.,  or  14,152  pounds  fine  copper.  During  an  ex- 
posure of  186  days,  the  ore  had  lost  34*3  per  cent  of  its  cop- 
per. 

"  All  the  experiments  made  on  a  total  of  nearly  3,000  tons 
of  ore  proved,  beyond  possibility  of  doubt,  an  average  loss  of 
more  than  one  unit  of  copper,  or  over  20  pounds  of  ingot  per 
ton  of .  ore.  This  great  loss  during  the  roasting  readily  ac- 
counted for  the  deficit  in  the  copper  production,  if  only  1J  per 
cent  was  deducted  from  the  assay  value  of  the  ores  for  losses 
by  treatment.  The  actual  loss  by  the  smelting  process,  as 
practiced  at  Ducktown,  approached  two  units.  Further  ex- 
periments were  made  to  confirm  the  results  obtained.  Experi- 
ments in  roasting  in  furnaces  proved  that  no  copper  escaped 
in  the  fumes.  This,  indeed,  was  anticipated,  as  the  heat  in 
roasting  never  could  reach  a  point  at  which  copper  is  volatile. 
The  only  other  possible  loss  is  by  the  leaching  of  the  roast- 
piles  during  the  heavy  rains  frequent  in  the  Ducktown  hills ; 
and  to  this  cause  the  great  losses  were  finally  ascribed.  In 
referring  to  experiments  in  the  leaching  of  these  ores  later  on, 
this  subject  will  be  discussed  in  detail.  Suffice  it  here  to  say, 
that  with  a  roasting  in  one  fire  only,  from  1  to  1^  units  of  cop- 


100     MODEKN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

per  become  soluble  in  water.  The  results  were  further  con- 
firmed by  copper  found  in  large  quantity  in  the  clay  •'  bottoms ' 
of  the  roast-piles.  After  a  shower  of  rain,  the  roast-yard  would 
be  covered  with  pools  of  green  water  highly  charged  with 
copper." 

The  cost  of  heap  roasting  was  estimated  at  80  cents  a  ton, 
including  the  transportation  of  the  ore  both  to  and  from  the 
roasting  ground,  as  well  as  its  weighing  and  other  slight  manip- 
ulations. The  expense  of  roasting  in  stalls  may  be  safely 
placed  at  54  cents  a  ton,  a  figure  based  on  the  actual  treat- 
ment of  many  thousand  tons  of  ore  by  this  method. 

The  cost  of  a  battery  of  56  stalls,  built  in  the  manner  rec- 
ommended, and  reduced  to  the  standard  table  of  prices 
adhered  to  throughout  this  work,  is  appended.  Their  life, 
under  ordinary  treatment,  will  not  exceed  six  years,  at  the  ex- 
piration of  which  time  they  will  be  found  in  such  a  condition 
as  to  demand  complete  rebuilding,  although,  of  course,  the 
stack  will  outlast  many  generations  of  stalls. 

ESTIMATED  COST  OF   56    ROASTING    STALLS,   EXCLUSIVE   OF    STACK. 

This  being  the  first  estimate  yet  given  pertaining  to  the 
construction  of  any  considerable  portion  of  a  smelting  plant, 
the  quickest  and  most  convenient  method  of  arriving  at  the 
desired  result  will  be  presented  a  little  more  in  detail  than 
may  be  considered  necessary  in  subsequent  calculations. 

The  total  expense  of  the  finished  stalls  may  be  con- 
veniently divided  into  the  following  heads  : 

1.  Excavation  for  foundations. 

2.  Cost  of  slag-brick,  clay,  and  other  building  materials, 
delivered  on  the  ground. 

3.  Labor  in  building  the  stalls. 

4.  Total  expense  of  the  railroads  belonging  to  this  part  of 
the  plant. 

5.  Miscellaneous  expenses  and  superintendence. 

The  actual  expense  of  building  a  plant  of  this  description 
will  almost  invariably  be  found  much  greater  than  the  most 
carefully  prepared  estimates  would  indicate,  unless  the  figures 
were  made  by  a  man  of  long  experience  in  these  matters.  The 
value  of  the  numerous  estimates  of  cost  and  expense  contained 


STALL  BOASTING.  101 

in  these  pages  is  principally  due  to  the  fact  that  they  are, 
almost  without  exception,  taken  from  the  results  of  actual 
work,  executed  under  the  superintendence  of  the  author.  They 
may,  consequently,  lay  claim  to  a  usefulness  and  reliability 
that  the  most  carefully  prepared  estimates  of  cost  would  not 
possess  unless  derived  from,  or  at  least  corrected  by,  a  long 
and  thorough  personal  experience  in  such  matters. 

To  prepare  the  foundations  for  the  required  number  of 
stalls,  assuming  the  ground  to  be  comparatively  level,  will  re- 
quire about  60  days'  labor,  aside  from  the  removal  of  the  earth. 
This  allows  for  an  8-inch  pavement,  and  for  an  extension  of 
the  foundation  walls  about  two  feet  under  ground. 

1.  Excavation  for  foundations  : 

Labor,  60  days,  at  $1.50  ...............................  $90.00 

Removing  the  excavated  material  ......................    35.00 

Superintendence  and  miscellaneous  extras  ...............    32.00 

Total  ............................................  $157.00 

In  order  to  estimate  the  amount  of  building  material  re- 
quired, it  is  essential  to  determine  the  cubic  contents  of  all  the 
walls  inclosing  the  56  stalls,  28  in  each  row.  The  stalls  being 
6J  feet  wide,  and  all  walls  being  32  inches  thick,  it  will  be  seen 
that  the  entire  length  of  the  two  main  rear  walls  is  520  feet,  to 
which  must  be  added  the  aggregated  length  of  the  58  parti- 
tion walls,  each  8  feet  long=464,  or  a  grand  total  length  of 
984  feet.  This  wall  being  6  feet  high  and  32  inches  thick, 
contains  in  round  numbers  15,700  cubic  feet.  To  this  must 
still  be  added  about  one-third,  to  allow  for  the  foundation  waUs, 
and  also  the  necessary  amount  of  slabs  for  paving  the  stalls. 
The  details  are  as  follows  : 


walls  ................................  15,700  slag-brick. 

Foundation  walls  ..........................    5,250    "       " 

Paving  ....................................    2,080     "       " 

Total  ..................................  23,030     "      " 

As  these  slabs  are  8  by  10  by  20  inches,  they  contain  very 
nearly  a  cubic  foot  each,  and  when  the  very  coarse  joints  that 
they  form  are  also  considered,  it  will  be  found  that  their  cus- 
tomary rating  of  a  cubic  foot  each  will  be  perfectly  safe.  They 
are  laid  entirely  in  ordinary  clayey  loam,  which  may  be  found 


102      MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

almost  everywhere,  and  which,  if  too  sticky  to  leave  the  trowel, 
will  be  greatly  improved  by  the  addition  of  one-fourth  or  more 
of  sand,  or  even  sandy  loam.  At  our  standard  of  prices,  $1  per 
ton  will  be  ample  for  such  material,  and  will  lay  one  hundred 
brick.  The  cost  of  the  slag-brick  has  been  placed  at  two  cents 
on  the  ground,  as  their  delivery  is  as  least  as  expensive  as 
their  manufacture.  The  sum  mentioned,  that  is,  two  cents 
apiece  delivered,  or  one  cent  at  the  furnace,  will  cover  the  cost 
of  making  and  trimming,  and  leave  enough  margin  to  occa- 
sionally replace  the  pattern  blocks  and  other  material  neces- 
sary for  their  production. 

2.  Cost  of  materials  for  mason  work  : 

23,030  slag-brick,  at  2  cents $460.00 

235  tons  clay,  at  $1 235.00 

Mortar-boxes,  hods,  screens,  etc 45.00 

Total $740.00 

The  persons  employed  for  this  work  should  on  no  account 
be  the  regular,  high-priced  brick  masons,  as  these  fare  but 
badly  in  handling  the  heavy,  brittle  slabs,  and  neither  like  the 
work  nor  are  able  to  earn  the  large  wages  that  they  invariably 
demand  and  receive.  The  proper  mechanics  for  this  work  are 
what  are  popularly  known  as  "  country  stone-masons,"  whose 
apprenticeship  at  building  stone  walls,  underpinning  barns 
and  houses,  etc.,  has  exactly  prepared  them  for  handling  such 
rough  and  heavy  material  as  that  under  discussion. 

Experience  in  this  particular  kind  of  construction  has 
shown  that  the  most  advantageous  distribution  of  the  force  is 
to  provide  each  stone-mason  with  two  immediate  helpers,  who 
assist  him  constantly,  bringing  the  slab,  placing  it  in  position, 
and,  in  fact,  doing  everything  excepting  the  spreading  of  the 
mortar  and  that  last  wedging  and  chinking  that  are  of  such 
vital  importance  in  the  proper  execution  of  work  of  this  de- 
scription. 

There  are  no  hod-carriers,  as  the  slabs  are  delivered  by 
wagons  at  the  point  most  convenient  to  the  workmen,  and  the 
mortar,  easily  and  rapidly  manufactured  from  the  materials 
already  mentioned,  is  brought  in  large  pails,  being  used  in 
immense  quantities  in  work  of  this  description,  although  every 


STALL   ROASTING.  103 

crevice  should  be  well  filled  with  small  fragments  of  rock  or 
slag,  called  "  spalls." 

It  lias  been  found  that  each  group  of  three  men,  as  de- 
scribed above,  will  lay  on  an  average  100  slag-brick  daily,  and 
not  more. 

3.  Labor  in  building  stalls : 

Estimate  for  laying  100  brick: 

One  stone-mason $3.00 

Two  laborers  at  $1.50 3.00 

Mixing  mortar  for  same 50 

Carrying  mortar  and  other  miscellaneous  labor 15 

Superintendence 35 

Total  for  100 $7.00 

Total  for  23,030  brick $1,612.00 

4.  Cost  of  Railroad   Tracks. — As   all  railroads  about   the 
works  should  be  of  the  same  gauge  and  pattern,  a  single  de- 
tailed estimate  will  determine  the  cost  per  foot  once  for  all. 
For  tracks  of  the  required  description,  having  a  22-inch  gauge, 
and  calculated  to  carry  a  net  load  of  1,800  pounds,  the  car 
weighing  an  additional  800  pounds,  a  good  quality  T  rail  of 
not  less  than  12  pounds  to  the  yard  should  be  selected  and 
well  fastened  in  place  by  a  spike  in  every  sleeper,  while  the 
abutting  ends  of  the  rails  should  be  firmly  secured  by  fish- 
plates, tapped  for  four  |-inch  bolts,  two  to  each  rail.     Unless 
the  bolt-holes  in  both  fish-plates  and  rails  can  be  bored  where 
ordered  in  such  a  manner  that  there  shall  be  no  doubt  of  their 
perfect  correspondence,  it  is  better  to  leave  the  plates  blank, 
and  bore  them  on  the  spot.     This  may  seem  a  slight  matter, 
but  its  neglect  sometimes  causes  serious  annoyance  and  delay 
in  outlying  districts,  and  the  boring  of  the  thin  fish-plates  is  a 
slight  task,  as  every  smelter  should  be  provided  with  a  boring- 
machine  run  by  power,  which  is  indispensable  for  sampling 
pig-copper,  and  will  be  found  generally  useful. 

The  sleepers  are  sawed  from  the  ordinary  timber  of  the 
country,  and  may  be  conveniently  ordered  of  the  following  di- 
mensions :  36  inches  long,  6  inches  wide,  and  4  inches  thick — 
containing  each  6  feet,  board  measure.  They  should  be  placed 
39  inches  apart  from  center  to  center,  and  last  almost  indefi- 


104     MODEKN  AMEEICAN   METHODS   OF  COPPEK  SMELTING. 

nitely,  as  the  sulphate  salts  with  which  they  become  impreg- 
nated prevent  their  decay. 

For  convenience  of  calculation,  the  estimate  will  be  based 
on  a  length  of  100  yards  of  track  : 

Weight  of  iron : 

200  yards  rails  at  12  pounds  =  2,400  pounds 
Spikes,  bolts,  and  fish-plates  =     115 

Total 2,515  pounds  x  3|  ceflts  =  $88.02 

Sleepers : 
125  containing  6  feet  each  =  750  feet  at  $25  per  M   =    18.75 

Labor : 

Grading,  laying  track,  ballasting,  etc $13.50 

Superintendence 6.00 

Total 19.50 

Average  allowance  for  curves  and  switches lb.63 

10  per  cent  for  incidentals 13.90 


$152.80 

We  may  therefore  accept  the  figure  of  $1.53  per  yard,  or 
51  cents  per  foot,  as  the  cost  of  a  tram-road  of  this  description, 
and  there  being  three  lines  of  track  required  for  the  stalls,  ag- 
gregating a  length  of  780  feet,  to  which  must  be  added  100  feet 
for  connections,  switches,  and  single  main  line  to  smelter,  we 
have  a  total  of  880  feet  at  51  cents  =  $441. 

Bails  for  long  curves  may  be  bent  cold ;  for  short  curves, 
they  must  be  slightly  heated ;  while  frogs,  points,  etc.,  require 
welding,  and  can  be  readily  constructed  in  any  ordinary  black- 
smith's forge. 

Great  care  should  be  taken  in  laying  the  track,  nor  should 
the  foreman  rest  satisfied  until  every  point,  frog,  and  guard- 
rail is  in  proper  position  and  has  the  precise  curve  necessary 
for  easy  passage  of  the  car  without  undue  friction  or  danger  of 
derailment.  It  is  scarcely  necessary  to  say  that  this  work 
can  only  be  properly  and  economically  executed  under  the 
direction  of  an  experienced  railroad  constructor. 

5.  Miscellaneous  Expenses  and  Superintendence. — Aside  from 
the  allowance  made  in  each  department  of  the  work  for  the 
above  purposes,  it  will  be  found  in  practice  that  a  consider- 
able additional  sum  is  required  to  cover  errors  in  construction, 


STALL  BOASTING.  105 

blacksmith  work,  and  various  incidentals,  as  well  as  general 
superintendence,  amounting  in  a  case  similar  to  the  above  to 

$211.00 
Cost  of  4-inch  brick  arch  to  cover  main  flue 137.00 

$348.00 
Summary. 

Excavation  for  foundations $157.00 

Materials  for  mason- work 740.60 

Labor  in  building  stalls 1,612.10 

Railroads 441.00 

Miscellaneous  and  superintendence 348.00 

Grand  total $3,298.70 

Uneven  ground,  bad  weather,  and  other  unfavorable 
causes  may  increase  this  sum  to  a  considerable  extent,  but  the 
figures  given  will  be  found  safe"  under  ordinary  circumstances 
and  with  strictly  judicious  and  economical  management. 

The  calcination  of  matte  in  ore  stalls  of  the  pattern  just 
described  is  by  no  means  impossible,  the  principal  difference 
between  its  treatment  and  that  of  ore  being  the  increased 
quantity  of  fuel  required — about  three  times  as  much.  A  con- 
siderable proportion  of  the  matte  will  be  fused  during  the 
operation,  and  another  large  fraction  scarcely  affected  by  the 
process ;  so  that  from  three  to  four  burnings  are  required  to 
effect  any  reasonably  perfect  desulphurization. 

This  practice  cannot  be  recommended,  as  much  better 
results  are  obtained  by  providing  the  stalls  with  grate-bars,  and 
preventing  the  radiation  of  heat  from  the  surface  by  means  of 
an  arched  brick  roof,  as  described  in  the  succeeding  chapter. 

THE   STALL  ROASTING   OF  MATTE. 

This  is  a  method  well  known  in  the  Eastern  States,  and 
practiced  first  in  this  country,  so  far  as  any  record  can  be 
found,  at  the  old  Kevere  Copper- Works  in  Boston,  and  in  more 
modern  times  at  Copperas  Hill  in  Vermont,  and  at  the  noted 
Vershire  mine  in  the  same  State,  where  some  sixty  or  seventy 
stalls  still  stand  in  a  greater  or  less  state  of  preservation.  The 
partial  suppression  of  the  excessively  disagreeable  fumes  gen- 
erated in  the  heap  roasting  of  this  substance ;  a  gain  of  at  least 


106      MODERN   AMERICAN  METHODS  OF  COPPER  SMELTING. 

one-third  in  the  time  of  treatment — no  unimportant  item  in  the 
handling  of  such  valuable  material ;  and  a  very  great  diminu- 
tion in  the  losses  caused  by  the  elements,  are  the  principal 
reasons  for  the  selection  of  stalls  in  preference  to  heaps.  On 
the  other  hand,  must  be  placed  a  heavy  investment  in  build- 
ings and  in  the  stalls  themselves,  with  their  flues,  stacks,  etc. 
The  mere  grate-bars  for  a  single  matte  stall  cost  in  the  neigh- 
borhood of  $75,  and  the  constant  repairs  that  are  peculiarly 
necessary  in  the  case  of  mason-work  saturated  with  the  pro- 
ducts of  volatilization,  and  racked  by  the  frequent  and  exten- 
sive fluctuations  in  temperature,  due  to  the  ever-recurring 
heating  and  cooling  of  the  interior,  render  them  a  somewhat 
expensive  portion  of  the  plant,  as  will  be  seen  in  detail  in  its 
proper  place. 

MANAGEMENT  OF  MATTE   STALLS. 

The  grate-bars  being  thoroughly  cleansed  and  freed  from 
all  clinkers  and  debris  of  the  preceding  operation,  and  replaced 
in  position,  and  the  brick  walls  forming  the  sides  and  back  of 
the  stall  receiving  a  fresh  coat  of  plaster  (clay)  where  neces- 
sary, a  layer  of  fuel  is  placed  upon  the  grate-bars,  and  the 
broken  matte  thrown  upon  this  by  means  of  a  closely  tined 
fork,  to  separate  the  fine  stuff,  which  is  scattered  over  the  top 
after  the  stall  is  filled  with  an  average  charge  of  from  five  to 
six  tons. 

The  fuel  employed  is  wood  in  4  or  6-foot  lengths,  and  split 
to  a  comparatively  uniform  size.  From  10  to  20  cubic  feet  are 
used  for  each  charge,  metal  of  low  grade  rich  in  sulphur  re- 
quiring less  fuel  than  the  higher  varieties  of  matte.  Experience 
has  taught  the  great  advantage  obtained  by  the  use  of  hard 
wood,  and  too  much  care  cannot  be  bestowed  upon  the  selec- 
tion of  the  fuel,  which  should  be  of  the  best  quality  and  thor- 
oughly seasoned,  as  the  result  of  the  operation  depends  to  a 
remarkable  extent  upon  the  quality  of  the  fuel  used. 

Matte  of  any  grade,  from  the  lowest  coarse  metal  to  the 
highest  quality  of  regule,  may  be  treated  in  these  stalls  with 
almost  equal  results  as  regards  desulphurization. 

The  stalls  are  always  covered  by  rude  sheds,  to  protect  the 
brick-work  from  the  weather,  and  should  be  paved  with  slag 


STALL   ROASTING.  107 

blocks,  flat  stone,  or,  much  better,  heavy  iron  plates,  as  the 
constant  hammering  that  it  must  undergo  during  the  spalling 
of  the  matte  and  the  breaking  of  the  huge  clinkers  that  form 
an  almost  necessary  accompaniment  of  this  process,  quickly 
destroys  any  other  description  of  pavement. 

The  results  of  desulphurization  by  this  method  being  no 
more  thorough  than  by  heap  roasting,  the  same  number  of 
burnings  is  necessary  as  in  the  latter  case,  and,  owing  to  the 
difficulty  of  removing  the  heavy  clinkers  from  the  walls  and 
grate-bars  of  these  little  furnaces,  as  well  as  the  constant  bill 
of  expense  for  repairs,  the  cost  of  the  process  is  about  the  same 
as  in  heap  roasting.  The  almost  complete  identity  of  the  two 
methods  in  this  respect  renders  any  further  details  of  expense 
unnecessary. 

The  imperfections  of  all  the  methods  of  roasting  matte  in 
lump  form,  as  well  as  the  great  waste  of  time  and  metal,  and 
the  annoyance  caused  by  the  fumes,  are  serious  objections,  and 
it  is  only  under  exceptional  circumstances  that  these  crude 
and  dilatory  methods  can  be  recommended.  In  nearly  all  ad- 
vanced works,  they  have  given  place  to  the  much  more  rapid 
and  perfect  method  of  calcination  in  reverberatory  furnaces. 

The  ordinary  dimensions  of  the  stalls  in  use,  now  or  for- 
merly, at  some  of  the  principal  works  in  this  country  are  as 
follows : 

Width 5  feet. 

Depth  (front  to  back) 6  feet. 

Depth  of  ash-pit 1  foot  6  inches. 

Height  from  grate  to  spring  of  arch 4  feet  8  inches. 

Thickness  of  division  walls 1  foot  4  inches. 

Thickness  of  rear  walls 1  foot  8  inches. 

Area  of  flue  opening  in  rear  wall 160  square,  inches. 

A  stall  of  this  size  will  contain  from  five  to  six  tons  of 
matte,  and  will  burn  for  four  days  at  the  first  firing,  and  for 
about  three  days  at  each  subsequent  operation. 

Where  three  burnings  take  place,  the  capacity  of  each 
matte  stall  may  be  placed  at  one-half  ton  daily,  and  the 
amount  of  wood  required  for  the  three  burnings  will  be  one- 
twelfth  of  a  cord  per  ton  of  ore. 

From  the  measurements  already  given,  aided  by  the  esti- 


108      MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

mates  for  brick-work  found  in  a  succeeding  chapter,  the  cost 
of  a  block  of  such  covered  stalls  may  be  easily  arrived  at ;  the 
covering  arch  consisting  of  a  9-inch  semicircle  of  red  bricks, 
and  the  main  flue  section  being  at  least  equal  to  the  combined 
area  of  the  flues  that  enter  it. 

The  anchoring  of  a  block  of  such  stalls  is  very  simple,  con- 
sisting of  longitudinal  f-inch  rods,  while  the  uprights  may  be 
iron  rails  or  stout  wooden  timbers.  Each  side  wall  should  also 
be  braced  from  front  to  back  in  the  usual  manner,  while  the 
front  wall  of  the  stall  is  a  temporary  structure  of  brick  laid 
loosely  upon  the  grate-bars  and  braced  with  a  few  lengths  of 
flat  iron.  Fire-brick  are  ordinarily  used  for  this  purpose, 
the  common  red  brick  of  which  the  entire  permanent  portion 
of  the  structure  is  built  being  too  light  and  fragile  to  stand 
the  repeated  handlings  and  the  fluctuations  of  temperature. 

Since  the  ordinary  charge  only  fills  the  stall  about  two- 
thirds  full  at  the  front,  and  slopes  up  against  the  rear  wall  to 
nearly  the  height  of  the  flue  opening  near  the  top  of  the  walls,  or 
even  in  the  arched  roof,  a  large  space  exists  between  the  upper 
edge  of  the  temporary  front  retaining  wall  and  the  high  semi- 
circular brick  roof.  Through  this,  the  sulphurous  fumes  and  the 
products  of  the  combustion  of  the  fuel  during  an  early  stage  of 
the  process  escape  in  such  clouds  as  to  render  the  atmosphere 
of  the  shed  unfit  for  respiration.  To  partially  obviate  this  dif- 
ficulty, a  sheet-iron  curtain,  suspended  by  wires  running  over 
a  pulley  in  the  roof,  and  furnished  with  a  counter-weight,  is 
used,  and  if  properly  fitted  and  luted  to  the  side  walls  with  a 
paste  of  stiff  clay,  is  of  great  service. 

It  may  be  assumed  with  safety  that,  by  the  process  of 
matte-roasting  in  lump  form — whether  executed  in  heaps  or 
covered  stalls — from  two-thirds  to  three-fourths  of  its  original 
sulphur  contents  is  eliminated,  by  not  less  than  three  consecu- 
tive burnings. 


CHAPTER  YE. 

THE  BOASTING  OF  OEE8  IN  LUMP  FORM  IN  KILNS. 

BY  the  term  kiln,  as  used  here,  we  understand  a  compar- 
atively small,  shaft-like  furnace,  provided  with  a  grate  or 
opening  for  the  admission  of  air  from  the  bottom,  and  con- 
nected with  a  draught  flue.  The  action  is  a  continuous  one, 
and  the  necessary  heat  is  derived  entirely  from  the  oxidation 
of  the  sulphur  and  the  other  constituents  of  the  ore. 

No  other  class  of  furnaces  has  received  greater  attention  or 
been  brought  to  a  greater  state  of  perfection  ;  but  it  is  as  an 
adjunct  to  the  manufacture  of  sulphuric  acid  rather  than  to  the 
calcination  of  ore  that  this  apparatus  must  be  esteemed,  and 
consequently  to  the  works  treating  on  that  subject  that  we  must 
look  for  detailed  descriptions  and  estimates  of  the  same.  The 
student  is  referred  to  Lunge's  exhaustive  work  on  Sulphuric 
Acid  for  full  details  of  construction  and  management. 

While  the  various  processes  of  roasting  hitherto  described 
are  suited  to  almost  every  variety  of  sulphureted  copper  ore, 
and  yield  equally  good  results  whether  the  percentage  of  sul- 
phur and  copper  is  small  or  large,  a  much  closer  selection  of 
material  is  indispensable  for  successful  roasting  in  kilns,  and 
their  range  of  usefulness  is  restricted  to  comparatively  narrow 
limits. 

This  very  question  of  selection,  however,  varies  greatly 
with  the  purpose  in  view,  and  depends  upon  whether  it  is  de- 
sired merely  to  desulphurize  a  given  ore  without  any  attempt 
to  utilize  the  volatile  products  of  oxidation,  or  whether  the 
manufacture  of  sulphuric  acid  is  to  be  combined  with  the  pro- 
cess of  roasting. 

The  conditions  necessarily  present  before  any  pyrites  can 
be  utilized  for  the  manufacture  of  sulphuric  acid  are  of  two 
kinds,  commercial  and  technical. 


110     MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

The  commercial  conditions  are  sufficiently  obvious  to  any 
thoughtful  mind,  and  are  very  plain,  such  as  sufficient  supply 
of  ore  at  a  fixed  and  low  rate  for  a  reasonable  length  of  time, 
and  contiguity  to  water,  railroads,  or  some  cheap  means  of 
transportation  to  the  manufactory,  which,  owing  to  the  nature 
of  its  product,  must  be  situated  in  the  immediate  vicinity  of  its 
market. 

The  technical  conditions,  though  more  numerous,  are  al- 
most equally  easy  of  comprehension.  An  almost  absolute  free- 
dom from  gangue  is  essential,  for  the  simple  reason  that  the 
presence  of  foreign  substances  lowers  the  percentage  of  sul- 
phur and  necessitates  the  handling  of  worthless  material,  thus 
lessening  the  capacity  of  the  works  and  producing  other  un- 
favorable results.  For  the  same  reason,  though  in  a  less  degree, 
the  presence  of  any  other  sulphides  but  the  bisulphide  of  iron, 
which  forms  the  ore  proper,  is  disadvantageous ;  for  no  other 
compound  of  sulphur  contains  either  so  high  a  percentage  of 
the  same  or  parts  with  it  so  freely.  Even  the  copper  pyrites, 
which  in  many  instances  forms  the  principal  value  of  the  ore, 
is  detrimental  to  the  manufacture  of  sulphuric  acid,  both  be- 
cause it  contains  less  sulphur  and  because  it  is  too  fusible  to 
permit  the  proper  regulation  of  the  temperature.  Beyond  the 
limit  of  eight  per  cent,  of  copper  in  the  pyrites,  it  cannot  be 
profitably  employed  in  the  manufacture  of  acid.  The  Spanish 
pyrites,  from  which  so  large  a  proportion  of  the  acid  produced 
in  England  is  made,  contains  on  an  average  about  three  per 
cent,  of  copper,  and  about  48  per  cent,  of  sulphur,  this  remark- 
ably high  percentage  of  sulphur  showing  its  freedom  from 
gangue. 

An  analysis  of  the  average  ore  from  the  celebrated  Rio 
Tinto  mine  may  be  of  interest,  as  a  type  of  a  very  favorable 
cupriferous  pyrite  for  acid  making  : 

ANALYSIS  OP  RIO  TINTO  PYRITES  BY  PATTINSON. 


Sulphur 48-00 

Iron 40-74 


Copper 3-42 

Lead 0'82 

Lime 0'21 

Total. .  10015 


Magnesia 0  08 

Arsenic 0'21 

Insoluble 5 '67 

Oxygen  and  moisture I'OO 


The  ore  used  by  three  large  acid- works  in  Boston  and  New 


THE   ROASTING  OF  ORES   IN  LUMP  FORM  IN  KILNS.       Ill 

York  is  obtained  principally  from  Canada,  some  thirty  miles 
from  the  Vermont  line,  and  although  somewhat  variable  in 
purity,  averages  about  3'5  per  cent  of  copper  and  45  per  cent,  of 
sulphur,  the  percentage  of  gangue  being  greater  than  in  the 
Spanish  ores. 

An  excellent  quality  of  pyrites  is  mined  from  a  large 
deposit  in  Western  Massachusetts,  and  in  both  Virginia  and 
Georgia  are  beds  of  pyrites  now  under  process  of  development, 
which,  on  competent  authority,  are  said  to  rival  the  Spanish 
mines  in  almost  every  particular. 

The  presence  of  arsenic  and  antimony  has  a  deleterious 
effect  on  the  quality  of  the  resulting  acid,  while  lead  heightens 
the  fusibility  of  the  charge  besides  wasting  sulphur  by  form- 
ing a  stable  lead  sulphate,  and  any  foreign  substance,  however 
harmless  otherwise,  lessens  the  percentage  of  sulphur. 

An  important  point,  sometimes  overlooked  by  non-profes- 
sionals in  determining  the  value  of  a  sample  of  pyrites,  is  its 
mechanical  behavior  during  the  process  both  of  crushing  and 
of  roasting.  A  granular  ore,  soft  or  easily  disintegrated,  will 
increase  the  proportion  of  fines,  which,  although  now  utilized 
with  great  success  in  the  manufacture  of  acid,  are  still  unde- 
sirable as  requiring  a  more  expensive  plant  and  entailing  a 
greater  cost  in  their  treatment.  A  still  more  serious  produc- 
tion of  fines  may  take  place  in  the  kiln  itself  in  the  case  of  ores 
that  decrepitate,  sometimes  occurring  to  such  an  extent  as  en- 
tirely to  choke  the  draught  and  render  their  employment  im- 
possible. 

One  of  the  most  serious  errors  ever  perpetrated  in  the  man- 
ufacture of  acid  from  pyrites  is  the  attempted  employment  of 
pyrrhotite  or  monosulphide  of  iron  for  pyrite — bisulphide  of 
iron.  Aside  from  the  greatly  lessened  proportion  of  sulphur, 
36  per  cent,  as  against  53  per  cent.,  the  monosulphide  will  not 
even  yield  freely  what  sulphur  it  contains,  but  crusts  with 
oxide  of  iron,  turns  black,  and  is  soon  extinguished  when 
treated  in  an  ordinary  pyrites  kiln.  It  seems  scarcely  possi- 
ble that  extensive  works  for  the  manufacture  of  sulphuric  acid 
(and  copper)  should  have  been  erected,  their  ore  supply  being 
entirely  derived  from  a  deposit  of  the  valueless  monosulphide ; 
but  such  has  been  the  case  in  more  than  one  instance,  and  will 


112      MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

continue  to  be  so  in  enterprises  conducted  without  the  aid  of 
skilled  direction.  One  of  the  most  striking  instances  of  this 
kind  is  a  now  extinct  Massachusetts  company,  which  is  said 
to  have  expended  over  $200,000  in  this  manner,  all  of  which 
was  a  total  loss,  excepting  the  small  amount  realized  from  the 
sale  of  buildings  and  lands. 

Under  certain  conditions,  the  use  of  kilns  for  the  calcina 
tion  of  cupriferous  pyrites  without  the  production  of  sulphuric 
acid  may  be  found  advantageous,  as  in  the  case  of  the  former 
Orford  Nickel  and  Copper  Company,  near  Sherbrooke,  Province 
of  Quebec,  which,  after  employing  heap  roasting  for  some  time, 
erected  a  large  number  of  kilns  solely  for  the  purpose  of  cal- 
cining its  ore  previous  to  smelting ;  finding  the  saving  in  time 
and  avoidance  of  waste,  combined  with  the  lessening  of  the 
annoyance  formerly  experienced  from  sulphur  fumes,  a  suf- 
ficient advantage  to  repay  the  somewhat  heavy  cost  of  the 
burners. 

The  minimum  percentage  of  sulphur  sufficient  to  maintain 
combustion  in  kilns  does  not  yet  seem  to  have  been  positively 
determined ;  but  with  an  ore  otherwise  favorable,  it  is  proba- 
ble that  25  per  cent  is  quite  sufficient  for  the  purpose. 

For  economy's  sake,  as  well  as  for  the  purpose  of  retaining 
the  heat,  kilns  are  constructed  in  blocks  of  considerable  length, 
and  of  the  depth  of  two  burners,  the  front  of  each  facing  out- 
ward, while  the  flue  in  which  the  gas  is  conveyed  to  its  desti- 
nation is  built  on  top  of  the  longitudinal  center  wall.  Fire- 
brick are  used  wherever  the  masonry  is  exposed  to  heat  or 
wear,  and  the  entire  block  of  furnaces  is  surrounded  by  cast- 
iron  plates,  firmly  bolted  in  position,  and  provided  with  the 
necessary  openings  for  manipulation. 

No  fuel  is  required  after  the  burners  are  once  in  operation  ; 
and  when  in  normal  condition,  the  attendance  demanded,  aside 
from  the  labor  connected  with  the  regular  charge  of  from  500 
to  2000  pounds  of  ore  once  in  twelve  or  twenty-four  hours,  is 
very  slight. 

Much  skill  and  experience,  however,  are  required  to  main- 
tain the  regular  working  of  the  kilns,  especially  with  ores  that 
are  not  exactly  suited  to  the  process. 

From  five  to  ten  per  cent,  of  fines  may  also  be  desulphur- 


THE  BOASTING  OF   ORES   IN   LUMP   FORM  IN   KILNS.       113 

ized  with  the  coarse  ore  without  seriously  interfering  with  the 
process.  They  are  thrown  toward  the  back  and  sides  of  the 
shaft,  leaving  the  center  uncovered";  otherwise,  the  draught  is 
affected  and  serious  irregularities  supervene. 

In  accordance  with  the  policy  adopted  throughout  this 
work,  no  detailed  estimate  of  expense  will  be  given  in  the  few 
instances  where  the  author  is  unable  to  base  the  same  on  per- 
sonal experience. 

Such  is  the  case  in  kiln  roasting ;  but  we  are  assured  by  the 
best  authorities  that  the  expense  of  calcination  by  this  method 
does  not  exceed  that  of  stall  roasting,  though  the  first  cost  of 
the  plant  is  considerably  greater. 

The  results  obtained  by  this  process  are  unexampled  in  the 
roasting  of  lump  ores,  although  there  is  no  doubt  that  a  con- 
siderable share  of  the  success  is  due  to  the  fact  that  the  sul- 
phur is  the  object  of  interest,  instead  of  merely  being  a  waste 
product  to  be  driven  off  as  far  as  convenient. 

If  more  than  4  per  cent,  of  sulphur  remains  in  the  cinders, 
as  the  residue  from  this  process  is  called,  the  result  is  not  con- 
sidered satisfactory.  It  is  needless  to  say  that  such  a  perfect 
desulphurization  cannot  be  obtained  in  either  heap  or  stall 
roasting,  nor  is  it  necessary  or,  in  many  cases,  even  beneficial 
for  the  subsequent  process,  although,  of  course,  in  most  in- 
stances the  lack  of  sulphur  in  the  furnace  charge  forms  a  wel- 
come outlet  for  the  admixture  of  raw  fines,  which  may  thus 
escape  the  expense  of  calcination. 

Within  the  past  few  years,  the  utilization  of  these  fines  has 
attracted  much  attention,  and  the  efforts  to  calcine  them  in 
automatic  furnaces  for  the  production  of  sulphurous  acid  have 
been  crowned  with  success,  as  will  be  again  alluded  to  when 
treating  of  the  Boasting  of  Pulverized  Materials. 

The  attempt  to  utilize  kilns,  with  certain  slight  modifica- 
tions, for  the  roasting  of  copper  matte  has,  after  many  difficul- 
ties and  much  expense,  attained  a  successful  issue  at  certain 
European  works,  especially  at  the  Mansfeld  copper-works  in 
Germany,  the  object  in  view  being  rather  the  abolition  of  the 
nuisance  arising  from  the  escape  of  the  sulphur  fumes  into  the 
atmosphere  than  any  expectation  of  financial  advantage  from 
the  employment  of  a  substance  so  poor  in  sulphur  for  the 
8 


114      MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

manufacture  of  acid.  It  is  obvious  that  only  mattes  compara- 
tively free  from  lead  and  other  fusible  metals  can  be  treated  in 
this  manner,  and  that  the  process  of  roasting  is  beset  with  dif- 
ficulties that  have  only  been  overcome  by  the  exercise  of  the 
greatest  skill  and  patience. 


CHAPTER  VII. 

CALCINATION    OF  ORE  AND  MATTE   IN   FINELY  DIVIDED  CONDITION. 

PERHAPS  the  most  marked  point  of  difference  between  the 
roasting  of  lumps  and  fines  is  the  time  requisite  for  their  oxi- 
dation. Oxidation  is  almost  instantaneous  for  an  infinitely 
small  particle  of  any  sulphide,  and  the  time  increases  with  the 
cubic  contents  of  the  fragment,  until  such  a  size  is  reached 
that  the  air  fails  to  penetrate  the  thick  crust  of  oxides  formed 
upon  the  outside  of  the  lump  of  ore  or  matte,  and  all  action 
ceases. 

.  It  might  seem,  therefore,  that  the  process  of  pulverization 
should  be  pushed  to  extreme  limits,  and  that  the  best  results 
would  be  obtained  from  the  most  finely  ground  ore.  But  this 
is  by  no  means  the  case  in  actual  practice ;  for  other  condi- 
tions arise  that  more  than  counteract  any  advantage  in  time. 
The  chief  of  these,  aside  from  the  difficulty  and  expense  in- 
volved in  the  production  of  such  fine  pulp,  are,  the  losses  in 
metal,  both  mechanical  and  chemical,  that  occur  with  every 
movement  of  the  ore,  and  reach  an  enormous  aggregate  before 
the  operation  is  completed ;  and  the  liability  to  fritting  or 
sticking  together  in  the  calcining-furnace,  regardless  of  the 
greatest  possible  care  in  this  process.  The  oxidation  of  the 
particles  takes  place  with  such  rapidity  that  a  temperature  is 
generated  above  the  fusion-point  of  ordinary  sulphides. 

Still  further  objections  could  be  mentioned;  but  those 
already  adduced  are  sufficient  to  limit  the  degree  of  pulveriza- 
tion for  the  principal  portion  of  the  ore,  although  a  greater  or 
less  proportion,  according  to  the  machinery  used  for  the  pur- 
pose, is  crushed  to  an  impalpable  dust,  and  causes  a  consider- 
able mechanical  loss,  in  spite  of  all  provision  for  its  prevention. 

The  best  size  to  which  to  crush  varies  with  each  individual 
ore,  and  is  entirely  a  matter  of  trial  and  experience;  nor 
should  any  one  responsible  for  the  calcination  of  any  given 


116      MODEEN  AMERICAN  METHODS   OF  COPPEE  SMELTING. 

material  rest  satisfied  until  he  has  determined  by  actual  and 
long-continued  experiment  that  the  substitution  of  either  a 
coarser  or  a  finer  screen  for  the  size  in  use  will  be  followed  by 
less  favorable  results. 

This  may  be  arrived  at  by  careful  comparative  determina- 
tions of  the  residual  sulphur  contents  after  the  calcination  of 
material  crushed  through  screens  of  various  sized  mesh  and 
roasted  for  the  same  length  of  time,  careful  consideration  also 
being  given  to  the  cost  of  crushing  in  each  case,  to  the  condi- 
tion of  the  oxides  of  iron  present  (the  sesquioxide  is  an  unfa- 
vorable constituent  in  reverberatory  smelting),  and,  above  all, 
to  the  quantity  of  flue-dust  formed,  and  loss  of  metal  by  vola- 
tilization. 

It  is  evident  that  such  diverse  and  obscure  questions  can 
only  be  accurately  determined  by  extensive  and  long-continued 
trials.  But  the  result  is  well  worth  the  labor,  and  in  these  days 
of  almost  universal  information  and  close  competition,  it  is  only 
by  such  means  that  any  decided  advantage  can  be  obtained. 

While  mattes,  speiss,  or  similar  products  of  fusion  must 
always  be  granulated  or  pulverized  to  the  degree  required  for 
calcination,  it  is  not  an  uncommon  quality  of  sulphide  ores 
either  to  decrepitate,  or  else  to  fall  to  pieces  when  heated,  by 
the  mere  moving  from  place  to  place  in  the  furnace,  to  such  an 
extent  that  the  charge  may  be  made  up  of  pieces  from  the  size 
of  a  walnut  down,  without  affecting  either  the  time  requisite 
for  the  oxidation  or  for  its  perfection.  The  product  will  be  an 
almost  homogeneous  and  impalpable  powder. 

A  more  striking  illustration  of  such  a  condition  of  affairs 
can  hardly  be  found  than  in  the  case  of  the  concentrates  from 
the  Parrot  Company's  mine  at  Butte,  Montana. 

In  this  instance,  the  process  of  subdivision  resulted  from 
two  different  causes.  The  iron  pyrites  that  forms  the  larger 
portion  of  the  ore  decrepitates  into  very  minute  cubes,  which 
are  subsequently  reduced  to  a  fine  powder  by  oxidation,  while 
the  fragments  of  pure  copper  ore — bornite — seem  gradually 
to  diminish  in  size  by  the  wearing  away  of  the  surface  as  it 
becomes  earthy  and  friable  from  the  superficial  formation  of 
oxides. 

This  latter  phenomenon  may  also  be  observed  to  a  less  ex- 


CALCINATION  OF  OEE  AND  MATTE.  117 

tent  in  the  calcination  of  mattes  when  they  are  of  a  sufficiently 
soft  or  porous  nature  ;  but  in  roasting  a  considerable  quantity 
of  a  very  low-grade  matte  (from  10  to  15  per  cent,  of  copper) 
that  had  been  obtained  in  hard  polished  granules  by  tapping 
into  water,  it  was  found  impossible  materially  to  alter  either 
the  size  or  shape  of  the  grains,  many  of  which  were  as  large 
as  an  army  bean,  or  satisfactorily  to  reduce  the  percentage  of 
sulphur,  even  by  long  exposure  to  a  temperature  closely  ap- 
proaching its  fusion-point. 

On  the  other  hand,  quite  satisfactory  results  are  obtained 
in  the  case  of  richer  matte  (from  30  to  40  per  cent,  of  copper) 
by  granulation  in  water ;  and,  in  many  of  the  foreign  works, 
this  is  the  only  means  provided  for  the  preparation  of  the 
matte  for  the  process  of  roasting  ;  but  it  must  be  remembered 
that  this  practice  is  confined  to  the  English  reverberatory 
method,  where  it  is  not  desired  to  remove  more  than  50  per 
cent,  of  the  sulphur  by  roasting,  and  where  a  portion  of  sul- 
phides still  remains  in  the  calcined  matte  that  would  be  en- 
tirely unsuited  to  the  so  called  "  blast-furnace  "  method  of 
matte  concentration  in  cupolas,  as  usually  practiced  in  this 
country. 

Although  the  results  described,  as  obtained  by  granulation, 
may  be  improved  upon  by  careful  attention  to  the  temperature 
and  pitch  of  the  matte  when  tapped,  and  especially  by  care 
and  experience  on  the  part  of  the  smelter,  this  practice  can- 
not be  recommended,  excepting  under  peculiar  conditions  and 
in  remote  situations,  where  improved  crushing  machinery  is 
not  obtainable,  or  where  the  physical  condition  of  the  matte  is 
particularly  favorable  to  the  production  of  porous  and  friable 
granules.  Nor  is  anything  gained  by  its  employment  fo  the 
purpose  of  avoiding  the  preparatory  breaker,  and  obtaining  at 
once  a  material  sufficiently  subdivided  for  immediate  treat- 
ment in  the  final  pulverizing  apparatus ;  for,  although,  in  this 
practice,  the  larger  granules  are  broken  and  crushed  into  a 
condition  favorable  for  the  calcining  process,  a  large  propor- 
tion of  the  entire  mass  is  already  so  minute  as  to  pass  through 
the  crashing  apparatus  untouched  in  the  shape  of  minute 
spherical  pellets  or  globules,  which  present  the  least  possible 
surface  to  oxidation,  and  retain  a  hard,  glossy  surface.  These 


118     MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

grains  are  scarcely  affected  by  any  moderate  temperature,  and 
may  even  undergo  complete  fusion  without  any  perceptible 
loss  of  sulphur.  Not  many  years  ago,  the  question  of  economy 
might  have  influenced  the  adoption  of  this  practice ;  but  at 
the  present  time,  and  in  view  of  the  improved  and  compara- 
tively inexpensive  machinery  at  our  disposal,  it  is  probable 
that  the  inconvenience,  danger,  and  other  drawbacks  insepara- 
ble from  the  projection  of  large  quantities  of  molten  sulphides 
into  water,  and  their  subsequent  recovery  from  the  reservoir 
or  whatever  vessel  is  employed  for  the  purpose,  more  than 
outweigh  the  cost  of  crushing  by  machinery. 

It  is  impossible  to  lay  down  fixed  rules  for  the  degree  of 
pulverization  of  any  material  best  suited  to  roasting.  Each 
case  must  be  decided  according  to  its  own  peculiar  conditions, 
including  the  cost  of  labor  and  power,  and  the  capacity  and 
quality  of  the  mechanical  means  available. 

Bearing  in  mind  the  results  that  may,  in  certain  excep- 
tional cases,  come  from  decrepitation,  it  may  be  assumed  that 
a  reduction  in  size  beyond  one  -twelfth  of  an  inch  is  seldom 
advantageous  in  treating  ores,  and  that  the  presence  of  a  large 
proportion  of  sulphides  or  of  a  particularly  porous  or  friable 
gangue  may  permit  an  increase  of  the  screen  mesh  to  one- 
eighth  inch  or  more.  With  mattes,  a  slightly  finer  standard 
(from  one-twelfth  to  one-sixteenth  inch)  may  be  employed. 

The  proportion  of  the  ore  reduced  to  a  minuteness  neither 
intended  nor  desired  depends  materially  upon  the  means  em- 
ployed for  crushing ;  and  as  the  mechanical  loss  and  other 
evils  enumerated  increase  in  direct  ratio  to  the  amount  of  fine 
dust  in  the  charge,  it  is  evident  that,  other  things  being  equal, 
the  apparatus  best  adapted  to  the  breaking  of  ore  or  matte  is 
that  which  produces  the  smallest  proportion  of  fines. 

CRUSHING  MACHINERY. 

The  crushing  machinery  used  for  the  purpose  under  dis- 
cussion may  be  divided  into  two  classes : 

1.  For    preparatory    crushing :    Jaw-breakers   of    various 
patterns. 

2.  For  final  pulverization  :  Stamps,  Ball  pulverizers,  Chili 
mills,  various  patent  pulverizers  and  grinders,  Cornish  rolls. 


CALCINATION   OF   OKE  AND   MATTE.  119 


I.   MACHINES  FOB  PREPARATORY  CRUSHING. 

The  jaw-crushers  in  almost  universal  use  are  eminently  sat- 
isfactory as  regards  economy,  capacity,  and  general  suitability 
to  the  purpose  for  which  they  are  intended.  A  few  deductions 
from  long-continued  trials  of  almost  every  well-known  pattern 
of  breaker  may  be  useful.  Ordinary  prudence  will  suggest  to 
the  inexperienced  the  choice  of  some  form  of  machine  long  and 
favorably  known  to  the  public,  and  nothing  can  be  more  foolish 
than  the  selection  of  some  novel  and  much  vaunted  but  untried 
apparatus. 

A  machine  should  be  selected  that  has  stood  the  test  of 
years,  and  is  manufactured  by  some  well-known  and  reputable 
firm.  Light-built  machines  should  be  particularly  avoided,  as 
the  strain  exerted  upon  certain  parts  of  every  breaker,  espe- 
cially when  clogged  with  clayey  ore  and  set  to  crush  fine  with- 
out shortening  the  stroke  of  the  jaw,  is  something  enormous, 
and  only  to  be  successfully  encountered  by  the  superabundant 
strength  in  every  portion  of  the  apparatus.  This  is  well  exem- 
plified in  the  breakers  turned  out  from  the  foundries  of  those 
manufacturers  who  have  long  made  a  study  of  this  particular 
business,  and  who  have  gradually  added  an  inch  of  metal  here 
and  a  half  inch  there,  as  time  and  trials  have  developed  the 
weak  points  of  the  machine,  until  it  may  appear  bulky  and 
clumsy  beside  the  light  and  elegant  models  of  some  of  their 
later  competitors.  Unless  ore  is  delivered  to  the  smelter  in 
unusually  large  lumps,  the  7  by  10-inch  jaw-breaker  will  be 
found  most  convenient  for  general  work,  and  not  so  heavy  as 
to  demand  special  arrangements  for  its  setting-up.  (These 
figures  refer  to  the  size  of  the  opening  between  jaws — the 
smaller  number  indicating  the  distance  between  the  fixed  and 
movable  jaw,  while  the  larger  gives  the  measurement  at  right 
angles  to  this.)  Such  a  machine  can  be  set  to  break  to  a 
maximum  diameter  of  three-quarters  of  an  inch,  and  has  a  ca- 
pacity equal  to  any  ordinary  demands,  although  varying  greatly 
with  the  size  of  the  discharge  opening  and  quality  of  the  ma- 
terial crushed.  The  setting-up  and  management  of  this  ma- 
chine are  matters  of  too  universal  knowledge  to  require  further 
attention ;  but  it  may  not  be  generally  understood  that  the 


120     MODEKN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

substitution  of  smooth  jaw-plates  for  the  corrugated  ones 
usually  employed  will  greatly  increase  the  proportion  of  fines 
in  the  product. 

As  the  ore  usually  passes  directly  from  the  breaker  to  the 
rolls — better  with  the  interpolation  of  a  short  screen  to  remove 
such  as  is  already  sufficiently  fine  ;  and  as  in  fine  crushing  the 
capacity  of  the  breaker,  even  when  set  up  to  its  closest  practi- 
cable limits,  usually  greatly  exceeds  that  of  the  rolls,  a  decided 
increase  in  the  work  performed  can  be  most  economically  and 
easily  effected  by  introducing  a  second  fine  breaker  between 
he  coarse  crusher  and  the  final  pulverizer.  This  machine 
may  be  of  quite  light  construction,  should  have  a  very  long, 
narrow  jaw  opening — say  2  by  12  inches — a  slight  "  throw," 
and  move  at  a  high  speed. 

It  is  in  this  direction  that  the  most  important  improve- 
ments in  fine  crushing  machinery  may  be  looked  for,  and  it  is 
probable  that  the  crushing  and,  still  more  important,  the  dis- 
charge area  may  be  most  advantageously  increased  by  the 
employment  of  a  multiple-jawed  machine.  This  apparatus — 
when  used  merely  as  an  intermediate  crusher — will  reduce  the 
product  of  the  coarse  breaker  to  the  size  of  corn,  or  even 
smaller,  thus  greatly  lightening  the  work  of  the  finishing  pul- 
verizer. 

H.  MACHINES  FOB  FINAL  PULVERIZATION. 

The  apparatus  at  all  suited  for  this  purpose  may  be  brought 
under  the  following  heads  : 

Stamps.  Miscellaneous  patent  pulverizers. 

Ball  pulverizers.  Multiple  jaw-crushers. 

Chilian  mills.  Cornish  rolls. 

Stamps,  although  universally  known  and  always  reliable, 
produce  far  too  great  a  proportion  of  fine  dust,  besides  being 
unnecessarily  expensive,  both  as  regards  first  cost  and  subse- 
quent running. 

The  Ball  pulverizer,  when  properly  constructed,  has  the 
merit  of  compactness,  slight  cost,  economy  in  running,  and  sev- 
eral other  advantages,  but  is  of  insufficient  capacity,  and,  like 
stamps,  is  better  calculated  for  the  production  of  fine  pulp  than 
of  the  material  required  for  calcination. 


CALCINATION  OF  OEE  AND  MATTE.  121 

Chilian  mills  have  obtained  a  strong  foothold  in  England  for 
certain  metallurgical  purposes,  but  are  expensive  and  cumber- 
some, have  a  very  small  capacity,  and  are  peculiarly  adapted 
to  the  production  of  impalpable  dust. 

The  miscellaneous  patent  pulverizers  now  offered  for  sale 
would  require  a  considerable  space  for  their  enumeration.  In 
many  cases,  they  possess  much  merit ;  but  although  differing 
to  an  extreme  in  almost  every  other  particular,  are  pretty  well 
united  in  producing  a  pulp  containing  too  much  dust  in  pro- 
portion to  the  granules. 

Multiple  jaw-crushers  have  already  been  referred  to  as 
promising  much  for  the  future.  This  construction  admits  of 
an  enormous  area  of  discharge  opening,  and  since  the  break- 
ing of  each  fragment  of  rock  is  accomplished  by  the  approach 
of  two  opposing  surfaces,  which  yet  can  never  meet,  all  parti- 
cles sufficiently  fine  are  at  once  removed.  There  is  reason  to 
hope  and  expect  that  these  machines  will  soon  be  perfected  ; 
in  which  case,  nothing  yet  invented  could  be  better  suited  to 
the  production  of  just  such  material  as  is  demanded  both  for 
concentration  and  for  the  variety  of  calcination  now  under  dis- 
cussion. 

Cornish  rolls. — No  other  class  of  machines  can  compare 
with  the  Cornish  rolls  for  capacity,  economy,  and  certainty  in 
crushing  every  variety  of  ore  and  matte  for  the  purpose  just 
indicated.  But  inasmuch  as  the  various  patterns  of  this  ma- 
chine differ  almost  as  much  among  themselves  in  efficiency  and 
capacity  as  they  do  from  the  other  pulverizers  already  men- 
tioned, and  as  an  examination  of  a  large  proportion  of  the 
roller  plants  in  actual  use  at  the  present  time  in  this  country 
indicates  a  great  want  of  care  in  both  construction  and  man- 
agement, and  tendency  to  be  satisfied  with  a  considerably 
lower  standard  of  excellence  than  might  easily  be  attained,  it 
seems  desirable  to  draw  attention  to  such  points  as  seem  to 
particularly  demand  supervision  or  reformation. 

Bolls  should  be  ordered  only  from  the  best  makers,  who 
can  refer  to  numerous  similar  machines  of  their  manufacture 
in  long  and  successful  operation,  nor  should  the  metallurgical 
engineer  forget  that  much  of  the  work  for  which  rolls  are  made, 
and  in  the  performance  of  which  they  give  perfectly  satisfac- 


122     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

tory  results,  is  for  phosphates,  gypsum,  lead  ore,  or  similar 
soft  or  brittle  substances,  whose  crushing  bears  no  relation 
to  that  of  the  low-grade  matte  and  tough  quartzoze — or  hard 
pyritic — ores  that  are  generally  the  object  of  calcination. 
Certain  low-grades  of  matte,  especially  when  produced  in  blast- 
furnaces, contain  a  large  proportion  of  various  indefinite  com- 
pounds of  copper,  iron,  and  sulphur  that  are  almost  malleable, 
and  would  inevitably  destroy  any  of  the  ordinary  light-weight, 
low-priced  rolls  so  frequently  considered  sufficient  for  general 
purposes,  and  occasionally  placed  in  metallurgical  establish- 
ments with  mistaken  notions  of  economy. 

The  most  important  proportions,  to  be  noticed  in  the  type 
of  rolls  required  for  the  purpose  under  discussion  are,  great  di- 
ameter of  the  body  of  the  roll  in  proportion  to  its  face — 2J,  or, 
better,  3  to  1 ;  great  strength  of  axle,  which  may  be  with  ad- 
vantage one-quarter  of  the  total  diameter  of  the  roll,  including 
shell ;  great  length  and  rigidity  of  bearings,  which  may  be 
of  Babbitt-metal,  or,  still  better,  of  brass ;  proper  size  and 
weight  of  fly-wheels,  and  a  general  strengthening  and  reinforce- 
ment of  all  parts  of  the  machine  that  are  found  weak  or  doubt- 
ful on  comparison  with  the  increased  capacity  of  the  portions 
just  named.  The  frame  in  particular  will  require  a  decided 
augmentation  of  strength  to  correspond  with  the  additions 
enumerated,  and  may  advantageously  be  cast  in  separate 
halves,  to  avoid  the  inconveniences  arising  from  its  bulk  and 
weight.  The  best  material  for  the  roll-shell,  as  well  as  the 
most  convenient  means  for  holding  the  two  massive  rolls  in 
apposition,  while  provision  is  yet  made  for  the  passage  of  any 
infrangible  or  incompressible  substance,  are  questions  that 
have  drawn  out  a  variety  of  opinion  and  practice. 

Two  varieties  of  shell  only  demand  consideration  for  the 
crushing  of  hard  ores  and  mattes. 

1st.  White  iron,  chilled  to  the  depth  of  nearly  an  inch,  and 
so  evenly  that  no  variation  in  wear  is  detected  on  the  surface 
after  the  passage  of  a  thousand  tons  or  more  of  the  hardest 
material. 

2d.  Soft  steel,  such  as  is  produced  by  the  Siemens-Martin 
method  at  a  very  moderate  cost. 

Such  chills  as  are  here  indicated,  and  as  are  alone  satisfac- 


CALCINATION  OF  ORE  AND  MATTE.  123 

tory  in  practical  work,  can  only  be  obtained  by  careful  manu- 
facture, and  the  ordinary  chilled  shells  advertised  as  perfectly 
satisfactory  by  the  greater  number  of  manufacturers  are  com- 
paratively worthless,  and  a  source  of  constant  annoyance  and 
expense.  A  pair  of  chilled  shells  of  36-inch  diameter,  14-inch 
face,  crushed  approximately  22,000  tons  of  medium  ore,  taking 
it  from  the  fine  breaker,  1J  inches,  and  reducing  it  to  about 
five-eighths  of  an  inch  in  size  before  being  worn  out,  the  chilled 
surface  wearing  smoothly  and  regularly  away  to  the  depth  of 
over  half  an  inch  before  any  notable  irregularities  appeared. 

It  is  always  advantageous  to  have  all  the  rolls  in  use  in 
any  establishment  of  the  same  diameter  and  make,  as  in  this 
way  a  very  great  saving  is  effected  by  using  all  new  shells  for 
fine  crushing,  and  when  too  much  worn  to  yield  economical 
results  in  this  situation,  to  pass  them  on  to  the  coarse  crush- 
ing rolls,  where  they  may  perhaps  serve  an  equally  long  time 
before  being  finally  discarded. 

It  is  by  no  means  generally  known  that  the  hardest  chilled 
iron  may  be  turned  with  an  ordinary  tool  without  difficulty  if 
a  sufficiently  slow  motion  is  made  use  of  in  the  process.*  In 
this  way,  a  set  of  shells  may  be  preserved  in  condition  for  fine 
crushing  for  a  much  longer  period  than  is  usual,  as  the  shells 
are  almost  invariably  incapacitated  for  this  purpose  by  their 
tendency  to  wear  hollow  in  the  center.  This  fault  may  be 
partially  obviated  by  a  simple  device  by  which  the  stream  of 
ore  as  fed  to  the  rolls  is  diverted  from  the  center  and  directed 
to  the  lateral  portions  of  the  roller  surface ;  but  is  much  more 
immediately  and  effectually  remedied  by  turning  the  surface 
smooth  under  the  precautions  just  indicated. 

Steel  shells  also  give  excellent  satisfaction,  and  are  quite 
easily  turned,  as  only  soft  steel  is  used  in  their  manufacture. 

No  one  who  has  watched  the  constant  jumping  of  all  ordi- 
nary rolls,  with  the  accompanying  separation  of  the  opposing 
surfaces,  and  has  noted  the  inevitable  escape  of  a  pound  or 
more  of  coarse  material  through  the  crevice  thus  formed,  can 

*  The  author  desires  to  acknowledge  his  indebtedness  to  Mr.  Franklin 
Farrel,  of  Ansonia,  Conn.,  for  this  important  point  in  the  manipulation  of 
chilled  iron,  as  well  as  for  many  novel  and  useful  suggestions  in  connection 
with  rolls  and  crushing  machines. 


124      MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

doubt  the  increase  in  capacity  that  would  arise  from  the  rigid 
fixation  of  the  crushing  surfaces  at  such  a  distance  from  each 
other  that  nothing  could  pass  between  them  without  being  re- 
duced to  the  desired  size.  Any  proposition  to  this  effect  is 
usually  met  with  the  objection  that  the  rolls  would  frequently 
become  "  stalled "  for  want  of  power,  or  else  that  constant 
breakages  would  arise  from  the  passage  of  a  bit  of  steel  or 
some  similar  infrangible  substance.  The  first  objection  is  too 
trivial  to  require  notice,  while  the  second  may  be  met  in  vari- 
ous ways :  By  either  increasing  the  strength  of  the  springs  by 
which  the  rolls  are  maintained  in  apposition,  to  such  an  extent 
that  no  substance  capable  of  being  crushed  with  detriment  to 
the  machine  can  pass  them  without  being  crushed;  or  by 
abolishing  springs  entirely,  and  providing  some  weak  point  in 
the  apparatus  that  shall  break  before  the  strain  becomes  dan- 
gerous to  other  and  more  expensive  parts. 

Both  of  these  methods  are  in  satisfactory  use,  the  latter, 
however,  being  suited  only  to  fine  crushing ;  the  employment 
of  a  thin  cast-iron  breaking-cup  renders  its  application  simple 
and  economical ;  while  the  former  improvement  is  best  effected 
by  the  use  of  strong  duplex  steel  car-springs,  or  heavy  rubber 
springs,  which  are  in  use  at  many  places,  giving  almost  univer- 
sal satisfaction. 

In  erecting  a  new  roller  plant,  provision  should  be  made 
for  convenience  in  changing  the  shells,  which  is  a  heavy  and 
tedious  task  unless  ample  space  is  reserved  overhead  for  the 
employment  of  block  and  tackle.  A  gain  of  several  hours  will 
be  effected  by  having  in  readiness  a  duplicate  set  of  roller- 
shafts  as  well  as  shells,  so  that  each  old  roll  may  be  lifted 
entire  from  its  bearings,  and  its  new  substitute  lowered  at  once 
into  the  vacant  place. 

Rolls  frequently  fail  to  meet  expectations  from  being  run  at 
too  low  a  speed.  Seventy-five  or  even  one  hundred  revolutions 
a  minute  for  a  36-inch  roll  is  not  too  great,  and  can  be  used 
with  no  untoward  results  beyond  the  increased  production  of 
fine  dust  from  the  violent  impact  of  two  solid  bodies  moving 
at  such  a  high  velocity. 

Unless  rolls  are  specially  constructed  for  the  purpose,  noth- 
ing is  gained  in  setting  them  so  that  their  surfaces  are  in 


CALCINATION   OF  ORE  AND  MATTE.  125 

direct  contact,  even  for  the  finest  crushing,  as  they  will  con- 
stantly choke  and  give  trouble,  without  yielding  nearly  as  large 
an  amount  of  product  of  the  desired  fineness  as  when  they  are 
set  slightly  apart,  and  the  product  that  is  not  fine  enough  to 
pass  the  screen  is  returned  to  them. 

Nearly  all  of  the  difficulties  and  annoyances  experienced 
with  elevators  may  be  avoided  by  constructing  them  with  a 
capacity  greatly  beyond  their  apparent  requirements. 

Strong,  large  cups  should  be  selected,  never  less  than  ten 
inches  in  width,  except  for  handling  very  fine  material,  and 
traveling  at  a  rate  of  at  least  280  feet  a  minute.  These  should 
be  strongly  riveted  to  a  four-ply  rubber  belt,  except  in  cases 
of  perfect  freedom  from  moisture,  where  leather  is  preferable. 

Double  chain  elevators  running  over  sprocket-wheels  also 
do  excellent  work  when  properly  made,  although  the  wear  is 
rapid,  and  little  or  no  saving  has  been  effected  by  their  em- 
ployment in  two  cases  under  the  writer's  management. 

The  feeding  and  management  of  the  crushing  plant  should 
be  intrusted  to  a  careful  and  experienced  man,  any  infraction 
of  this  rule  being  almost  certainly  followed  by  annoyance  and 
loss. 

Its  capacity  varies  greatly  with  the  quality  of  the  material 
and  the  fineness  to  which  it  is  crushed,  diminishing  very  rap- 
idly with  the  degree  of  comminution. 

As  a  rough  indication  of  what  may  be  expected  from  the 
variety  of  plant  just  indicated,  consisting  of  a  7  by  10-inch 
breaker,  and  a  single  pair  of  36-inch  rolls,  with  screen  and 
elevator,  the  following  figures  are  given  from  the  author's 
note-book :  A  hard  but  brittle  siliceous  ore,  carrying  a  small 
percentage  of  pyrites,  was  crushed  through  an  8-mesh  screen 
at  the  rate  of  2,236  pounds  an  hour.  The  substitution  of  a 
12-mesh  screen  reduced  the  hourly  production  to  1,560 
pounds. 

A  hard  and  tough  matte  was  crushed  through  the  latter 
screen  at  the  rate  of  only  960  pounds  an  hour,  nor  can  a  much 
greater  duty  than  the  above  be  expected  from  any  similar 
plant. 

Any  estimate  of  machinery  and  of  such  portions  of  the  gen- 
eral plant  as  can  be  purchased  ready  for  use,  and  conse- 


126     MODEEN  AMEEICAN   METHODS   OF  COFFEE  SMELTING. 

quently  possess  a  specific  market  value,  public  to  all,  does  not 
come  within  the  scope  of  this  treatise. 

CALCINING  FURNACES. 

The  furnaces  suited  especially  to  the  oxidizing-roasting  of 
sulphureted  ores  and  mattes  in  a  pulverized  condition  may  be 
included  under  the  following  heads  : 
I.  Shaft-furnaces. 
II.  Revolving  cylinders. 

III.  Automatic  reverberatory  furnaces. 

a.  With  stationary  hearth. 

b.  With  revolving  hearth. 

IV.  Ordinary  reverberatory  furnaces. 

a.  Open-hearth  furnaces. 
J.    Muffle  furnaces. 

I.   SHAFT-FURNACES. 

This  group  includes  some  of  the  most  important  and  useful 
appliances  for  the  roasting  of  sulphureted  substances,  where 
the  utilization  of  the  fumes  for  the  manufacture  of  sulphuric 
acid  forms  a  part  of  the  process  of  calcination. 

If  the  question  of  acid  manufacture  be  left  entirely  out  of 
consideration,  and  the  comparative  economy  of  each  method 
of  calcination  be  judged  solely  upon  its  own  merits,  it  is  doubt- 
ful whether  resort  would  be  had  to  these  furnaces,  save  under 
exceptional  conditions  ;  as  their  limited  capacity,  great  cost  of 
construction,  and  imperfect  work,  except  under  the  most  skill- 
ful management,  would  effectually  bar  their  introduction.  But 
under  the  stimulus  arising  from  the  enforced  manufacture  of 
acid  from  pulverized  pyrites,  and  the  consequent  necessity  of 
employing  some  form  of  automatic  furnace  in  which  the  gases 
arising  from  the  oxidation  of  the  ore  are  kept  separate  from  the 
products  of  combustion  of  the  fuel,  this  type  of  calciner  has 
received  such  attention  and  study  that  it  promises  fairly  to 
rival  the  most  economical  form  of  roasting  apparatus  known  to 
metallurgy.  The  student  is  referred  to  Lunge's  work  on  the 
manufacture  of  sulphuric  acid  for  full  details  regarding  this  and 
other  forms  of  furnace  suited  to  the  calcination  of  ores  in  con- 
nection with  acid -making. 


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CALCINATION  OF  ORE  AND  MATTE.  127 

The  Gerstenhofer  shelf-furnace  was  the  first  successful  cal- 
ciner  *  of  this  type,  and  is  still  largely  used,  though  becoming 
gradually  supplanted  by  improved  modifications.  The  few 
furnaces  of  this  pattern  that  have  been  constructed  in  the  United 
States  have  failed  to  answer  the  desired  purpose,  owing  to  im- 
perfect construction,  poor  refractory  materials,  and  want  of  skill 
in  management.  The  Gerstenhofer  furnace  consists  of  a  vertical 
shaft,  surmounted  by  a  mechanical  device  for  feeding  the  pul- 
verized sulphides  in  any  desired  quantity,  and  containing  a 
great  number  of  parallel  clay  ledges  of  a  triangular  form,  one  of 
the  flat  surfaces  being  placed  uppermost.  These  are  so  arranged 
as  to  obstruct  the  ore  in  its  passage,  and  delay  it  sufficiently 
to  effect  a  certain  degree  of  oxidation,  which  is  seldom  perfect 
enough  to  yield  the  desired  result  without  a  supplementary 
calcination  in  some  other  form  of  furnace.  The  front  wall  of 
the  shaft  is  pierced  by  parallel  rows  of  rectangular  openings, 
for  the  purpose  of  changing  the  clay  shelves  or  of  cleansing 
the  same. 

The  oxidation  of  the  sulphides  generates  sufficient  heat  for 
the  proper  working  of  the  process,  so  that  the  sulphurous 
gases  may  be  obtained  for  the  manufacture  of  acid  free  from 
any  products  of  the  combustion  of  fuel. 

The  Stetefeldt  furnace,  so  invaluable  for  the  chloridizing- 
roasting  of  silver  ores,  is  a  shaft  provided  with  a  grate  for  the 
generation  of  such  a  degree  of  temperature  as  would  be  lacking 
in  the  roasting  of  ores  so  poor  in  sulphur  as  those  usually  ex- 
posed to  this  treatment,  as  well  as  an  auxiliary  fire-place  for 
the  more  perfect  chloridizing  of  the  flue-dust,  which,  owing  to 
the  fine  pulverization  of  the  ore  and  the  strong  draught  essen- 
tial to  the  proper  working  of  the  apparatus,  is  formed  in  un- 

*  As  this  treatise  is  intended  to  deal  exclusively  with  American  methods 
and  practices,  any  detailed  description  of  various  valuable  automatic  cal- 
ciners  that  in  other  countries  have  proved  highly  successful  is  necessarily 
omitted.  Nor  will  consistency  permit  the  accurate  description  of  certain 
American  inventions — such  as  the  Stetefeldt  and  Howell  roasting- furnaces — 
which,  although  invaluable  for  the  chloridizing-roasting  of  silver  ores,  or 
even  for  the  thorough  calcination  of  fine  pyrites  for  clilorination,  have  not 
yet  been  adopted  to  any  considerable  extent  by  the  copper  smelter.  This  is 
of  the  less  consequence,  as  full  descriptions  of  all  these  various  forms  of 
apparatus  are  accessible  to  the  public. 


128     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

precedented  amounts,  and  pretty  thoroughly  regained  in 
ample  dust-chambers. 

The  employment  of  an  auxiliary  fire-place,  and  the  inven- 
tion of  a  highly  ingenious  and  perfect  automatic  ore-feeder, 
constitute  important  claims  to  originality  that  are  frequently 
overlooked  by  writers  in  commenting  on  this  furnace.  Its 
capacity  is  very  great,  60  tons  in  twenty-four  hours  being  easily 
worked  in  one  of  the  large-sized  furnaces  of  this  type ;  and 
were  it  possible  to  obtain  equally  good  results  by  employing 
it  for  oxidizing-roasting,  it  would  be  the  most  valuable  addi- 
tion to  the  modern  metallurgy  of  copper.  But  as  it  is  at  the 
present  time,  it  cannot  be  enumerated  among  the  resources  of 
the  copper  smelter,  although  late  experiments  indicate  the 
probability  of  its  successful  adaptation  to  this  purpose. 

The  English  acid-makers  have  introduced  various  modifica- 
tions of  the  two  last-named  furnaces  for  the  desulphurization 
of  cupriferous  iron  pyrites.  These  may  be  found  in  Lunge's 
work,  and  are  said  to  possess  considerable  capacity  and  yield 
excellent  results. 

H.    REVOLVING  CYLINDERS. 

These  also  are  extensively  and  advantageously  used  for  the 
chloridizing  of  silver  ores,  having  a  considerable  capacity,  and 
effecting  a  thorough  chloridization  at  a  very  moderate  cost. 
They  consist  essentially  of  a  horizontal  or  inclined  brick- 
lined  iron  cylinder,  revolved  slowly  by  gearing,  and  having  a 
fire-place  at  one  end — or  at  both  ends,  used  alternately. 

Numerous  experiments  as  to  their  applicability  to  the  oxi- 
dizing-roastiog  of  pyritous  ores  have  been  carefully  carried  out, 
and,  while  the  author  has  not  found  it  economical  for  this  pur- 
pose in  its  original  form,  late  experiments  with  the  double  cyl- 
inders lately  recommended  by  Mr.  Bruckner  have  seemed  to 
show  that  they  can  be  made  very  economical  for  the  calcina- 
tion of  sulphide  ores. 

A  still  further  advance  has  been  made  by  Mr.  James 
Douglas,  who,  by  introducing  an  interior  central  flue  for  the 
passage  of  flame  and  smoke,  and  carefully  graduating  the  sup- 
ply of  air,  has  combined  the  advantages  of  the  revolving  cylin- 
der and  the  muffle  furnace. 


130     MODERN  AMERICAN   METHODS   OF   COPPER  SMELTING. 


m.   AUTOMATIC  HEARTH  FURNACES. 

a.  With  Stationary  Hearth. — This  subdivision  is  best  rep- 
resented by  O'Hara's  mechanical  furnace,  which  differs  only 
from  an  ordinary  reverberatory  calciner  by  being  provided  with 
an  automatic  stirring  apparatus.  This  consists  of  two  or  more 
endless  chains,  to  which  are  fastened  at  regular  intervals  plow- 
shaped  scrapers,  which  traverse  the  long,  narrow  hearth  longi- 
tudinally, thus  stirring  the  ore  and  constantly  presenting  fresh 
surfaces  to  the  action  of  the  air.  This  furnace  has  found  little 


FIG.  2.— SPENCE  DESULPHURIZING  FURNACE. 

favor  with  copper  metallurgists.  The  expense  of  maintaining 
the  stirring  apparatus  in  proper  condition  at  the  comparatively 
high  temperature  to  which  it  is  exposed,  as  well  as  the  fact  that 
the  firing  of  the  furnace,  together  with  the  supervision  of  the 
machinery  and  motive  power,  requires  nearly  as  much  labor 
as  the  management  of  an  ordinary  calciner,  is  sufficient  to 
prevent  its  introduction. 

The  Spence  automatic  desulphurizer  is  a  more  promising 
member  of  the  same  division,  and  is  in  very  successful  operation 
at  a  number  of  acid-works  near  New  York  where  copper-bear- 
ing iron  pyrites  are  used. 


CALCINATION   OF   ORE  AND   MATTE. 


131 


From  a  paper  read  at  the  Philadelphia  meeting  of  the 
American  Institute  of  Mining  Engineers,  the  following  cut 
and  details  regarding  this  furnace  are  taken: 

Fig.  1  shows  the  double  furnace  in  perspective  ;  the  space 
occupied  by  it  being  34  feet  by  18  feet.  When  two  double 
furnaces  are  coupled  together  and  run  by  one  engine  (as  pre- 
ferred in  all  cases),  the  space  required  is  34  feet  by  32  feet. 
A  building  40  feet  by  40  feet  is  therefore  necessary  to  accom- 
modate this  plant  with  a  shed-roof,  if  connection  is  made  to 
towers  and  chambers,  or  an  ordinary  flat-roof  building  with 
supporting  posts  placed  between  the  furnaces,  when  connected 


FIG.  3.— SPENCE  DESULPHURIZING  FURNACE-SECTION. 

directly  with  the  chimney,  as  in  the  process  of  desulphurizing 
gold  ores.     Fig.  2  is  a  longitudinal  section. 

There  are  several  practical  points  of  excellence  about  the 
furnace  (which  has  been  in  operation  near  New  York  for  the 
past  three  months)  that  entitle  it  to  careful  examination  by 
engineers.  The  action  of  the  furnace  will  be  understood  to  be 
automatic,  the  ores  being  elevated  from  the  furnace-floor, 
brought  in  from  the  floor  above,  or  by  other  means  supplied  in 
quantities  as  required  to  keep  the  hoppers  full.  This  matter 
of  detail  will  readily  be  understood  by  those  practiced  in  the 
handling  of  ores  from  different  levels,  and  the  drying  of  the 
ores  (if  wet)  will  also  be  understood  to  be  a  simple  matter  when 
small  quantities  are  regularly  fed. 


132     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

The  hoppers  being  filled,  a  small  auxiliary  engine  is  started, 
and  by  means  of  a  changeable  gear,  properly  connected,  opens 
the  valves  to  start  the  pair  of  engines  shown  in  the  foreground 
of  Fig.  1. 

These  engines,  having  7-inch  by  12-inch  cylinders,  and  run- 
ning at  40  revolutions  per  minute  (giving  a  minimum  of  wear 
and  tear  for  the  service  performed),  quietly  and  positively  oper- 
ate by  means  of  geared  wheels  the  rods  to  which,  in  the  fur- 
nace, are  attached  toothed  rakes  (Fig.  2). 

The  rods  are  very  firmly  held  in  place  and  position  by  the 


FIG.  4.— SPENCE  FURNACE  ;  CKOSS-SECTION. 


FIG.  5.— SPENCE  FURNACE  KABBLE. 


rack,  which,  supported  at  its  rear  end  by  wheels,  travels  along 
a  railroad. 

The  movement  of  the  rack  (with  rakes  inside  the  furnace) 
opens  the  ports  for  the  admission  of  fresh  ore  from  the  hoppers 
to  the  first  shelf,  and  the  discharge  of  finished  or  calcined  ore 
from  the  lower  shelf  into  cars.  When  the  rakes  have  finished 
the  forward  stroke,  the  engines  reverse  automatically,  and  the 
rack  returns  to  and  stops  in  position. 

The  auxiliary  engine  continues  running,  and  at  stated  times 
(determined  by  the  manager)  again  starts  the  large  engines, 
another  operation  of  stirring  and  raking  with  feed  and  discharge 
of  ores  taking  place. 

This  automatic  and  regular  method  of  feed  and  treatment 
of  the  ore  on  the  bed  of  the  furnace  is  the  result  of  years  of 


CALCINATION   OF   ORE   AND   MATTE.  133 

study  and  practice,  directed  to  the  object  of  replacing  by  a  uni- 
form mechanical  procedure  the  discretionary  operation  of  hand 
labor. 

By  study  of  the  plant  now  in  operation,  the  following  con- 
clusions are  reached  : 

1.  The  constituent  elements  of  the  ores  being  first  deter- 
mined, the  feed  and  discharge  are  regulated  to  exact  amounts 
in  pounds,  and  the  number  of  charges  fed  into  the  furnace  is 
duly  registered. 

2.  The  auxiliary  engine  being  set  to  start  the  motive  power 
say  every  five  minutes,  and  the  time  required  for  the  forward 
and  back  stroke  being  say  one  and  a-half  minutes,  it  follows 
that  the  interior  parts  of  the  rakes  are  exposed  to  action  of 
heat  and  acid  fumes  but  one-third  of  the  time,  thus  approxi- 
mating manual  labor  in  wear  and  tear  of  plant. 

3.  The  draught  of  air  being  regulated  and  controlled  by  the 
chemist  at  will,  insuring  the  proper  oxidation  of  the  ores,  and  no 
more,  less  chamber  space  must  be  required  than  by  any  other 
process  of  burning  pyrites,  and,  moreover,  no  special  care  need 
be  given  to  location  of  plant,  since  strong  winds  or  variable 
currents  can  have  no  effect  in  causing  "  blow-outs  "  of  gas  at  the 
doors. 

4.  The  movement  of  the  ores  from  the  hoppers  to  the  dis- 
charge-opening is  accomplished  by  a  system  of  reversed  teeth, 
which  are  positive  in  action. 

The  deterioration  or  destruction  of  cast-iron  rakes  and  teeth 
has  been  reduced  to  a  minimum  by  the  simple  but  novel  idea  of 
burying  the  parts  in  ore,  which  accumulates  at  the  front  of  the 
furnace-beds  when  the  rakes  are  at  the  position  of  rest. 

5.  Pyrites  "  smalls,"  such  as  are  found  in  Virginia,  at  the 
Milan  or  Capelton  mines,  carrying  47,  45,  and  40  per  cent,  of 
sulphur  respectively,  can  be  calcined  with  two  double  Spence 
furnaces,  run  by  one  engine  at  the  rate  of  from  15,000  to  20,000 
pounds  per  day  of  twenty-four  hours,  the  cinders  containing 
from  1^  to  2J  per  cent,  of  sulphur. 

It  is  claimed  that  larger  amounts  of  "  smalls  "  containing 
copper,  blende,  etc.,  can  be  put  through,  and  double  the  above 
quantity,  where  sulphur  fumes  are  passed  directly  into  the  air 
— as  would  be  the  case  in  working  auriferous  concentrates. 


134     MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

6.  Where  necessity  exists  for  bringing  the  sulphur  contents 
of  cinders  from  iron  pyrites  (FeS2)  down  to  J  to  ^  per  cent,  to 
utilize  the  iron,  or  for  the  like  treatment  of  rich  gold-bearing 
sulphurets,  the  result  is  accomplished  by  the  addition  of  a  tire- 
place  to  the  lower  hearth.     This  is  shown  in  Fig.  1,  although 
not  ordinarily  used. 

By  this  means,  the  proper  heat  is  kept  in  the  ores  until  they 
are  discharged  into  iron  cars  ;  but  in  general  working,  the  ores 
are  "  dead  "  on  the  lower  shelf. 

7.  The  average   cost  of  calcining  ores  by  this  automatic 
furnace  is  not  greater  than  by  any  other  method  at  present  in 
use. 

The  cost  of  the  furnace,  complete,  with  power,  is  about  the 
same  as  that  of  the  equivalent  grate-bar  space  in  kilns,  or  equal 
burning  space  in  the  present  type  of  shelf-furnaces. 

There  are  running  at  Bridgeport,  Connecticut,  one  double 
furnace  ;  at  Gowanus  Bay,  Long  Island,  two  double  furnaces ; 
at  Elizabethport,  New  Jersey,  two  double  furnaces ;  and  others 
are  building. 

b.  With  Movable  Hearth. — In  this  type  of  furnace,  the 
slowly  revolving  hearth  is  of  a  circular  and  conical  shape,  and 
may  consist  of  two  or  more  stories,  a  series  of  stationary  rakes 
being  fastened  above  each  in  such  a  manner  that  the  ore- charge 
is  thoroughly  stirred  at  frequent  intervals. 

The  Parke  furnace  and  the  Brunton  calciner  are  perhaps 
the  best  known  specimens  of  this  type,  and  have  been  some- 
what extensively  used  in  England  for  desulphurizing  purposes. 
Their  great  weight,  cost  of  construction,  and  heavy  repairs 
must  certainly  go  far  toward  counterbalancing  the  slight  sav- 
ing in  labor  claimed. 

IV.    REVERBERATORY    CALCINERS. 

a.  With  Open  Hearth. — This  division  includes  virtually  all 
of  the  calciners  in  every-day  use  in  this  country  for  the  cal- 
cination of  copper-bearing  sulphides  where  neither  the  man- 
ufacture of  sulphuric  acid  nor  other  outside  issue  has  influ- 
enced the  choice  of  apparatus. 

The  essential  features  of  the  ordinary  reverberatory  calciner 


CALCINATION   OF   ORE  AND   MATTE.  135 

are,  a  hearth,  heated  by  a  fire-place,  from  which  it  is  ordinarily 
separated  by  the  bridge-wall,  and  accessible  by  certain  open- 
ings through  the  side  walls,  the  whole  being  covered  by  a  flat 
arch  against  which  the  flame  reverberates  in  its  passage  from 
the  grate  to  the  flue,  thus  being  brought  momentarily  in  con- 
tact with  the  ore  spread  upon  the  hearth,  while  the  combined 
gases  from  fuel  and  charge  pass  into  the  open  air  through  a 
chimney,  in  many  cases  first  traversing  a  series  of  flues  and 
chambers  for  the  purpose  of  retaining  such  particles  of  metal 
as  may  have  been  either  chemically  or  mechanically  borne  away 
by  the  rapid  draught. 

A  very  small  grate  surface,  as  compared  with  the  hearth 
area,  distinguishes  this  type  from  the  reverberatory  smelting- 
furnace,  and  corresponds  to  the  very  moderate  temperature 
suited  to  the  process  of  calcination,  permitting  its  almost  entire 
construction  of  common  red  brick. 

A  single  detailed  account  of  the  longest  and  largest  variety 
of  calciner  in  common  use  will  serve  as  a  model  for  all  smaller 
specimens  of  the  same  class. 

The  principal  variable  dimension,  of  a  copper  desulphuriz- 
ing furnace  is  its  length,  as,  for  economical  reasons,  its  width 
should  always  be  as  great  as  is  compatible  with  convenient 
manipulation.  Experience  has  placed  this  limit  at  16  feet  for 
the  inside  measurement  of  the  hearth,  nor  should  this  dimen- 
sion be  lessened  without  good  and  sufficient  reasons. 

The  length  of  the  hearth  is  limited  chiefly  by  the  capacity 
of  the  ore  to  generate  heat  during  its  oxidation,  the  immediate 
influence  of  the  fire-place  being  seldom  capable  of  maintaining 
the  requisite  temperature  upon  a  hearth  over  16  feet  in  length, 
without  resorting  to  the  use  of  a  forced  blast,  or  of  a  draught 
so  powerful  as  greatly  to  increase  the  loss  in  dust  as  well  as 
the  consumption  of  fuel. 

The  importance  of  the  heat  generated  by  the  oxidation  of 
sulphides  in  maintaining  a  proper  temperature,  and  especially 
in  conveying  the  heat  to  a  great  distance  from  the  initial  point, 
is  seldom  fully  realized.  Its  intensity  and  durability  depend 
upon  the  percentage  of  sulphur  in  the  ore,  and  also  not  a  little 
upon  the  manner  in  which  it  is  chemically  combined,  the  bisul- 
phides— such  as  iron  pyrites — furnishing  a  much  greater 


136     MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

amount  of  heat  than  monosulphides  containing  an  equal  gross 
amount  of  sulphur. 

An  ore  carrying  less  than  10  per  cent,  of  sulphur  will  not 
furnish  sufficient  heat  to  warrant  the  addition  of  a  second 
hearth  to  the  first  16  feet,  which  will  be  assumed  as  the  normal 
length  of  a  single  hearth.  (Such  a  condition  would  scarcely 
occur  in  practice,  as,  under  ordinary  circumstances,  any  copper 
ore  containing  such  a  low  percentage  of  sulphur  could  be 
smelted  raw.)  An  increase  of  sulphur  to  15  per  cent.,  however, 
will  be  sufficient  to  heat  the  second  hearth,  while  a  20  per  cent, 
sulphur  ore  should  work  rapidly  in  a  three-hearth  furnace. 
The  addition  of  a  fourth  and  final  section  is  rendered  justifi- 
able by  the  increase  of  the  average  sulphur  contents  of  the  ore 
to  25  per  cent.,  and  even  a  20  per  cent,  bisulphide  charge  may 
be  worked  to  advantage  in  the  same. 

The  adoption  of  this  method  of  roasting,  by  which  the  ore 
is  fed  into  one  end  of  the  furnace,  and  gradually  moved  to  the 
other  extremity  before  discharging,  is  attended  with  several  ob- 
vious advantages  ;  among  which  are  :  The  gradual  elevation  of 
temperature  from  a  point  compatible  with  the  easy  fusibility 
of  the  unaltered  sulphides  to  that  degree  necessary  for  the  com- 
plete decomposition  of  the  pertinacious  basic  sulphates  of  cop- 
per and  zinc  ;  the  great  saving  in  fuel  effected  by  thus  obtain- 
ing the  full  benefit  of  the  heat  generated  in  the  process  of 
roasting  itself ;  the  certainty  that  the  charge  must  undergo  a 
certain  number  of  thorough  stirrings  and  turnings  in  its  trans- 
portation over  so  extended  a  space ;  the  establishment  of  a 
fixed  duty,  which  must  be  performed  by  the  workmen,  whose 
labor  can.  thus  be  much  more  easily  controlled  than  with  the 
single-hearthed  type  of  calciner,  where  the  attendants  can  easily 
substitute  an  idle  scratching  for  the  vigorous  manipulation  nec- 
essary to  move  the  ore  forward  promptly ;  a  great  simplification 
in  firing,  it  being  only  necessary  in  the  long  furnace  to  main- 
tain an  even,  high  temperature,  while  with  the  single  hearth, 
much  experience  and  judgment  are  required  to  adapt  the  heat 
to  the  ever-varying  condition  of  the  charge ;  lastly,  a  decided 
economy  in  construction,  the  ratio  of  fire-brick  to  common  red 
brick  for  an  equal  capacity  of  plant  being  much  less  in  the 
employment  of  long  furnaces. 


CALCINATION  OF  OEE  AND   MATTE.  137 

As  there  seems  to  be  almost  no  limit  to  the  extent  of  sur- 
face over  which  the  requisite  temperature  may  be  obtained  in 
the  calcination  of  highly  sulphureted  ores,  it  is  very  natural 
that  experiments  should  have  been  made  with  still  longer  fur- 
naces than  any  yet  mentioned,  120  feet  being  the  extreme  in- 
side length  yet  attempted,  so  far  as  known  to  the  writer  ;  but 
careful  and  repeated  trials  have  shown  beyond  a  doubt  that  no 
sufficient  advantage  is  reaped  to  pay  the  increased  cost  of  the 
inclosing  building  and  other  expenses  of  plant.  It  is  not  pos- 
sible for  two  attendants  properly  to  manage  a  furnace  having 
more  than  four  full-sized  hearths,  if  the  latter  is  pushed  to  its 
full  capacity,  while  the  addition  of  a  fifth  hearth  demands  a 
third  laborer,  whose  time,  however,  will  not  be  fully  occupied, 
while  a  sixth  hearth  will  overtax  the  three  workmen.  In  short, 
the  testimony  of  many  excellent  metallurgists,  to  which  the  au- 
thor can  add  his  own  experience,  unequivocally  condemns  the 
lengthening  of  ordinary  calcining-furnaces  beyond  the  limits 
above  indicated,  excepting  under  special  and  peculiar  condi- 
tions. 

The  number  of  working-doors  to  a  long  calcining-furnace, 
where  the  ore  is  moved  from  rear  to  front,  should  be  as  few  as 
possible.  The  limit  for  comfortable  work  should  not  exceed 
eight  feet  between  centers  of  doors,  and  any  distance  less  than 
six  feet  is  a  decided  disadvantage. 

The  sides  of  the  working-door  frames  should  have  short 
lugs,  not  exceeding  six  inches  in  length,  cast  on  them,  in  order 
that  they  may  be  firmly  held  in  position  by  the  buckstaves, 
which  are  placed  in  pairs  for  this  purpose,  a  single  buckstaff 
being  placed  in  the  center  of  the  space  between  each  pair. 
The  bottom  of  the  door-frames  should  be  on  a  level  with  the 
hearth  surface,  which  should  be  three  feet  above  the  floor 
grade  of  the  building,  which  should  slope  gradually  upward 
toward  the  rear  of  the  furnace,  to  correspond  with  the  increased 
height  of  each  succeeding  hearth. 

The  common  practice  of  filling  up  the  portions  of  the  hearth 
between  the  working-doors  with  projecting,  triangular  masses 
of  brick-work  cannot  be  recommended,  as  valuable  space  is 
often  sacrificed  in  this  manner.  Slight  projections,  as  shown 
in  the  accompanying  cut,  may  be  built  to  fill  the  absolutely  in- 


138     MODERN  AMERICAN  METHODS   OF   COPPER   SMELTING. 

accessible  angles ;  but  with  properly  constructed  door-frames, 
and  careful  manipulation  on  the  part  of  the  roasting  attendants, 
but  little  waste  area  should  exist,  and  this  will  regulate  itself 
by  becoming  filled  with  ore,  which  may  remain  there  perma- 
nently. This  refers,  of  course,  to  the  treatment  of  large  quanti- 
ties of  low-grade  ores,  where  slight  inaccuracies  resulting  from 
the  trifling  mixture  of  ores  can  do  no  harm. 

After  raising  the  side  walls  to  the  height  required  by  the 
iron  door-frames,  usually  about  ten  inches  above  the  hearth 
level,  the  skewback  for  the  main  arch  should  be  laid.  This 
applies  to  the  entire  furnace  from  the  beginning  of  the  fire-box 
to  the  extremity  of  the  rear  hearth,  and  is  a  very  simple  mat- 
ter, especially  if  the  arch  is  to  be  perfectly  horizontal,  as  is  to 
be  recommended  in  most  cases.  A  taut  line  should  be 
stretched,  to  insure  accurate  work,  and  if  red  brick  are  used, 
they  should  be  cut  on  one  long  edge,  being  laid,  of  course, 
longitudinally  and  on  the  flat.  They  should  be  cut  at  an  angle 
slightly  greater  than  required  by  the  curve  of  the  arch,  which 
should  rise  about  three  quarters  of  an  inch  to  the  foot,  making 
a  sixteen-foot  arch  twelve  inches  higher  in  the  center  than  at 
the  sides.  This  rise,  though  less  than  is  often  recommended, 
will  be  found  ample  to  insure  perfect  safety  and  durability,  and 
will  tend  to  spread  the  flame  and  heat  toward  the  sides  of  the 
hearth. 

If  so-called  "  side  skewback "  fire-brick  are  within  reach, 
they  should  be  used  in  place  of  the  red  brick,  saving  much  cut- 
ting and  insuring  a  better  job.  Three  rows,  in  height,  of  red 
brick,  or  two  of  fire-brick,  will  give  a  solid  bearing,  the  total 
number  required  for  a  furnace  of  the  size  under  consideration 
being  respectively  600  and  375. 

It  is  of  sufficient  importance  to  bear  repetition,  that  all  por- 
tions of  the  mason  work  above  the  hearth  line,  or  wherever  ex- 
posed to  heat,  must  be  laid  in  clay — common  brick  clay,  tem- 
pered with  sand,  being  quite  good  enough  for  all  portions  of 
the  furnace — as  fire-clay  is  usually  expensive  in  the  localities 
where  copper  ores  abound. 

Lime  mortar,  much  improved  by  the  admixture  of  a  little 
of  certain  cements — say  10  percent. — may  be  advantageously 
employed  for  the  outside  work,  and  wherever  there  is  no  dan- 


CALCINATION  OF  ORE  AND  MATTE.  139 

ger  of  heat,  as  it  makes  handsomer  and  stronger  work,  and  is 
greatly  preferred  by  the  masons,  who  require  constant  super- 
vision to  compel  them  to  use  clay  mortar  where  it  is  neces- 
sary. 

The  heavy  iron  bridge  plate,  so  indispensable  in  reverber- 
tory  smel ting-furnaces,  may  be  entirely  omitted,  the  bridge 
being  built  up  solid  and  covered  on  the  top  and  sides  with 
fire-brick,  with  the  exception  of  a  longitudinal  opening  3  by  8 
inches,  which  should  penetrate  it  from  one  end  to  the  other, 
communicating  with  the  outside  air  on  each  side  of  the  fur- 
nace, and  with  the  hearth  by  some  half-dozen  2  by  4-inch 
openings. 

By  this  means,  heated  air  free  from  all  reducing  gases  is 
admitted  into  the  furnace  below  the  sheet  of  flame  that  sweeps 
over  the  top  of  the  bridge.  The  oxidizing  effect  of  this  .cur- 
rent of  air  is  very  powerful,  and,  as- frequently  determined  by 
experiment,  hastens  materially  the  calcining  process. 

If  wood  is  used  as  a  fuel,  an  additional  row  of  similar 
openings  should  be  constructed  in  the  arch,  immediately  over 
the  front  line  of  the  bridge-wall,  by  which  a  much  more  per- 
fect combustion  of  the  gases  is  effected.  With  coal  as  a  fuel, 
the  latter  openings  are  superfluous,  provided  the  firing  is 
properly  managed. 

Aside  from  the  sixteen  working-door  frames,  and  the  ordi- 
nary doors  for  fire-box  and  ash-pit,  no  castings  are  necessary 
for  the  entire  structure,  excepting  a  small  frame  to  protect  the 
charging-hole,  which  should  be  situated  a  little  back  of  the 
center  of  the  rear  hearth,  being  placed,  of  course,  in  the  me- 
dium longitudinal  lino  of  the  furnace.  It  will  add  also  mate- 
rially to  the  durability  of  the  fire-box  to  surround  the  portions 
of  the  same  most  exposed  to  pressure  or  mechanical  violence 
by  light  cast  plates,  held  in  place  by  the  uprights. 

As  the  portion  of  the  hearth  immediately  beneath  the 
charging-hole  is  exposed  to  excessive  wear  from  the  constant 
precipitation  of  heavy  masses  of  wet  material  upon  it,  an  area 
some  three  feet  square,  and  in  the  locality  designated,  should 
be  constructed  of  either  fire-brick  or  slag  blocks,  the  latter, 
from  their  texture  and  general  physical  condition,  being  pecu- 
liarly well  suited  to  the  purpose. 


140     MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

By  referring  to  the  accompanying  sketch,  it  can  be  plainly 
seen  at  what  stage  in  construction  the  various  bearing  bars 
and  other  iron  work  must  be  inserted. 

It  will  be  noticed  that,  instead  of  adopting  the  ordinary 
large  ash-pit,  entirely  open  at  the  rear,  according  to  the  inva- 
riable English  practice,  preference  is  given  to  a  closed  ash-pit, 
to  which  air  is  admitted  by  a  door  at  one  or  both  ends.  This 
effects  a  great  saving  in  fuel,  and  brings  the  process  of  com- 
bustion more  perfectly  under  control.  Comparative  tests, 
extending  over  a  considerable  period  of  time,  show  this  saving 
to  amount  to  about  50  per  cent,  of  the  entire  fuel  consumed, 
in  the  case  of  coal,  and  about  65  per  cent,  (in  volume)  when 
pine  wood  is  used.  The  tight  ash-pit  becomes,  of  course,  a 
matter  of  positive  necessity  where  anthracite  coal,  with  a 
forced  blast,  is  used. 

The  side  and  end  walls  having  been  carried  up  to  the 
required  height,  and  the  skewback  constructed  on  both  sides 
for  their  entire  length,  the  carpenters  take  possession  tempo- 
rarily, usually  under  the  supervision  of  the  head  mason,  to 
put  in  the  wooden  center  on  which  the  arch  is  to  be  built.  If 
a  second  furnace,  or  indeed  any  other  work,  is  available  for 
the  remaining  masons,  it  is  advantageous,  though  not  indis- 
pensable, to  permit  the  furnace  to  stand  uncovered  for  several 
days,  thus  allowing  the  mortar  to  set,  and  greatly  increasing 
the  strength  of  the  mason  work. 

Having  selected  for  description  that  pattern  of  calciner  in 
which  the  gradual  diminution  of  the  space  between  arch  and 
hearth,  as  it  recedes  from  the  grate,  is  due  to  successive  slight 
elevations  of  the  hearth  level,  instead  of  the  ordinary  down- 
ward pitch  of  the  roof,  it  is  evident  that  the  arch  throughout 
its  entire  extent  will  be  horizontal,  while  all  four  inclosing 
walls  are  built  up  to  the  same  height  at  every  point,  with  the 
exception  of  a  rectangular  flue-opening  in  the  rear  wall,  6  by 
30  inches. 

The  construction  of  the  wooden  pattern  or  center  is,  there- 
fore, extremely  simple,  requiring  only  some  20  pieces  of  2-inch 
plank,  16  feet  long  and  14  inches  wide  ;  a  lot  of  2  by  4  scantling, 
to  form  posts  about  10  inches  in  length,  four  of  these  being 
needed  to  support  each  plank  on  edge ;  and  finally,  a  sufficient 


CALCINATION  OF  OKE  AND  MATTE.  141 

amount  of  4-inch  battens,  from  one-half  to  one  inch  thick,  to 
cover  the  area  of  the  required  roof,  when  placed  about  three- 
quarters  of  an  inch  apart.  The  plank  should  be  perfectly 
sound,  and  at  least  partially  seasoned. 

By  the  aid  of  a  long  rod,  moving  upon  a  pivot  at  one  end, 
while  the  free  extremity  carries  a  pencil,  a  segment  of  a  circle 
corresponding  to  a  rise  of  12  inches  in  the  center  of  the  length 
of  16  feet,  should  be  struck  on  each  plank,  and  the  line  fol- 
lowed accurately  with  a  jig-saw. 

The  segments  for  that  portion  of  the  arch  over  the  bridge 
and  fire-box  are  shorter,  of  course,  than  those  belonging  to  the 
main  hearth,  but  should  be  got  out  in  the  same  manner,  and 
then  shortened  at  each  end  to  the  required  length. 

The  scantling  should  be  cut  into  posts  somewhat  shorter 
than  necessary  to  bring  the  curve  on  the  upper  edge  of  the 
segments  to  the  proper  height  for  the  lower  surface  of  the 
arch,  so  that  each  post  may  be  wedged  to  an  exact  bearing 
with  thin  slips  of  wood.  It  is  quite  necessary  that  the  weight 
should  be  evenly  distributed,  and  each  segment,  when  brought 
into  correct  position,  is  held  there  by  driving  a  nail  through 
a  longitudinal  line  of  battens  in  the  center  and  at  each  ex- 
tremity. 

The  segments  for  sloping  arches  should  be  still  further 
strengthened  by  short  braces  toe-nailed  obliquely  from  the 
upper  edge  of  one  strip  to  the  lower  edge  of  its  neighbor,  and 
so  on  throughout  the  entire  frame. 

An  omission  of  this  precaution  has  caused  the  canting  of 
the  segments  and  consequent  destruction  of  a  large,  nearly 
completed  arch  under  the  author's  charge. 

No  difficulty  will  be  experienced  in  removing  the  wooden 
pattern  in  good  condition  for  further  use,  provided  it  is  sup- 
ported on  small  posts  as  just  described ;  but  if  long,  heavy 
blocks  of  timber  are  used  as  a  foundation  for  the  segments, 
great  labor  as  well  as  much  injurious  sledging  must  accompany 
their  removal,  resulting  usually  in  the  complete  destruction  of 
both  segments  and  battens.  In  fact,  where  this  method  of  sup- 
port has  been  practice^,  it  will  be  found  best  to  burn  out  the 
inclosed  patterns,  after  the  tie-rods  are  properly  tightened, 
closing  both  damper  and  ash-pit  so  as  to  allow  only  a  slow 


142     MODERN   AMERICAN  METHODS   OF   COPPER  SMELTING. 

smoldering,  and  prevent  any  injurious  rise  of  temperature  in 
the  still  damp  furnace. 

Few  jobs  of  mason  work  require  more  care  and  conscien- 
tiousness than  the  laying  of  a  large  calciner  arch,  as,  owing  to 
its  great  width  and  slight  curvature,  a  very  little  lack  of  close- 
ness in  its  myriad  joints  would  be  sufficient  to  allow  it  to  yield 
to  the  enormous  pressure  brought  to  bear  by  its  own  weight, 
and  become  sufficiently  compressed  to  slip  down  between  its 
side  walls.  It  is  quite  a  simple  matter  to  lay  a  good  solid  arch 
of  fire-brick,  owing  to  their  great  regularity  and  smoothness 
and  almost  perfect  rectangular  form ;  but  when  red  brick  are 
used,  which  vary  so  in  size  and  thickness,  and  are  so  fre- 
quently warped  out  of  all  reasonable  shape,  much  care  is 
required. 

In  ordinary  calciners,  it  is  customary  to  construct  that  por- 
tion of  the  arch  from  the  fire  end  of  the  furnace  to  a  point  mid- 
way between  the  first  and  second  working-doors  of  fire-brick, 
nine  inches  in  thickness,  the  brick  standing  endwise.  At  this 
point,  or  even  considerably  sooner,  when  necessary,  red  brick 
are  substituted,  being  placed  also  on  end,  and  each  brick, 
after  being  dipped  into  a  pail  of  liquid  clay  mortar,  being 
pressed  closely  against  its  neighbor,  and  finally  settled  into 
position  with  a  few  light  blows  of  the  hammer. 

Moderately  soft  brick  are,  as  a  rule,  best  suited  to  this  .pur- 
pose, although  they  must,  of  course,  possess  ample  solidity  to 
resist  the  compression  to  which  they  are  exposed.  Hard- 
burned  brick,  though  stronger,  are  too  irregular  and  warped 
to  be  often  used  in  a  large  arch,  and  in  any  case  the  brick 
should  be  all  carefully  selected  beforehand  by  the  attendant, 
and  assorted  in  such  a  manner  that  each  longitudinal  row — 
extending  the  entire  length  of  the  furnace — is  composed  of 
brick  of  about  the  same  thickness. 

Another  most  important  precaution  is  the  preservation  of 
the  proper  angle,  as,  in  order  to  establish  the  required  curve, 
each  row  must  incline  slightly  from  the  vertical,  the  lower 
ends  of  the  bricks  being  in  contact,  which  is  not  the  case  with 
their  upper  extremities. 

The  establishment  and  preservation  of  the  proper  curvature 
are  facilitated  by  the  occasional  interpolation  of  a  longitudinal 


CALCINATION   OF   OKE   AND  MATTE.  143 

row  of  wedge-shaped  or  key -brick,  technically  called  "bull- 
heads." These  are  usually  only  obtainable  made  from  fire- 
clay, but  are  almost  indispensable  for  the  center  row,  when 
the  final  keying  of  the  arch  is  effected.  Otherwise,  the  entire 
row  of  key-brick  must  be  cut  from  common  brick,  an  arduous 
and  imperfect  task. 

The  keying  is  a  matter  of  some  delicacy,  and  should  be 
performed  by  a  single  workman,  who  should  select  or  cut  his 
keys  of  such  thickness  as  to  produce  a  uniform  moderate  pres- 
sure throughout  the  entire  distance,  no  more  force  being  ex- 
erted to  drive  the  key  into  place  than  can  be  easily  effected  by 
a  light  mason's  hammer,  using  an  intervening  block  of  wood 
to  prevent  the  destruction  of  the  brick. 

While  the  masons  are  thus  employed,  the  blacksmith  and 
his  helper  should  have  completed  the  buckstaves  and  tie-rods 
from  measurements  furnished  by  the  foreman  mason  as  the 
work  progresses,  it  being  in  such  cases  easier  to  suit  the  length 
of  the  tie-rods  to  the  completed  mason  work,  than  to  pursue 
the  opposite  course. 

As  soon  as  the  arch  is  completed,  the  head  mason  and 
blacksmith  should  proceed  to  the  ironing  of  the  furnace, 
which,  with  the  assistance  of  two  laborers,  should  be  com- 
pleted in  a  single  day. 

The  most  convenient  and  easily  obtained  buckstaves  in 
most  cases  are  old  iron  rails  of  full  size,  say  80  pounds  to  the. 
yard.  Properly  shaped  beams,  of  corresponding  strength, 
are  about  15  per  cent,  lighter.  The  tie-rods  may  consist  of 
inch  round-iron  for  the  bottom  rods,  and  inch  and  a  quarter 
iron  for  the  upper  rods.  The  lower  rods  are  already  long  in 
place,  and  through  each  of  their  loops  should  now  be  slipped 
one  of  the  upright  buckstaves,  cut  to  the  proper  length,  and 
temporarily  wedged  into  the  loop  to  keep  it  perpendicular. 

The  upper  tie-rods  may  be  made  the  same  as  the  lower, 
with  a  loop  at  each  end — the  necessary  tightening  being 
effected  by  flat  iron  wedges;  or  they  may  have  a  threaded 
extremity  at  one  end  passing  through  a  corresponding  hole 
in  the  buckstaff,  and  fitted  with  a  strong  nut ;  or,  best  of  all, 
a  small  ring  is  formed  at  one  end  of  the  tie-rod,  through  which 
slips  a  U-shaped  piece  of  round  iron,  which  fits  against  the 


144      MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

buckstaff,  on  the  other  side  of  which  a  piece  of  flat  iron, 
pierced  with  two  holes  for  the  free  ends  of  the  U,  is  held, 
these  ends  being  threaded ;  a  nut  for  each  of  the  ends  com- 
pletes the  apparatus,  and  presses  the  piece  of  flat  iron  tight 
against  the  upright.  This  is  a  simple  and  highly  satisfactory 
device,  and  avoids  the  disagreeable  process  of  wedging  in  the 
one  case,  or  of  punching  a  large  hole  through  a  narrow  rail  in 
the  other.  The  strain  is  distributed  over  two  bolts  and  nuts, 
and  can  be  instantaneously  increased  or  diminished  ;  nor  will 
the  nuts  rust  solid  into  place,  provided  they  are  saturated  with 
oil  annually,  and  slightly  turned,  to  free  them. 

Whatever  method  of  tightening  the  tie-rods  may  be  selected, 
the  process  of  ironing  or  anchoring  should  begin  with  the 
first  tie-rod  on  the  main  body  of  the  furnace,  nearest  the  fire 
end,  and  proceed  systematically  toward  the  rear,  thence  re- 
turning to  the  shorter  transverse  rods  that  support  the  arch 
over  the  grate,  and  terminating  with  the  long  longitudinal 
rods,  which,  for  convenience  of  handling,  should  be  in  three 
lengths,  connected  with  hooks  and  eyes.  Up  to  this  time,  no 
great  strain  should  be  put  upon  the  rods,  everything  being 
merely  brought  to  a  solid  bearing ;  but  after  all  are  in  place, 
and  the  buckstaves  evened  both  vertically  and  laterally,  the 
rods  may  be  drawn  to  the  desired  tension,  the  skewback  being 
still  further  supported  by  a  bar  of  one  by  four  inch  flat  iron, 
or,  better,  an  iron  or  steel  rail,  let  in  flush  with  the  brick- 
work. 

This  is  largely  a  matter  of  experience,  and  being  of  vital 
importance,  should  receive  the  most  careful  attention  on  the 
part  of  the  builder,  as  too  lax  a  condition  of  the  rods  may 
permit  the  entire  falling  in  of  the  arch,  while  the  contrary 
fault  may  cause  a  positive  buckling  and  elevation  of  the  same, 
accompanied  with  a  general  cracking  and  distortion  of  the 
lateral  walls.  The  latter  accident,  in  a  moderate  degree,  is 
much  more  likely  to  occur  than  the  former,  owing  to  the  nat- 
ural tendency  to  overdo  a  measure  essential  to  safety,  and  yet 
not  exactly  defined. 

The  lateral  rods  should  be  tightened  until  they  begin,  when 
struck  near  the  center  with  a  hammer,  to  vibrate  rapidly,  and 
to  be  but  little  depressed  when  stepped  upon.  (It  is  almost 


CALCINATION  OF  OKE  AND   MATTE.  145 

needless  to  say  that  none  of.  the  upper  rods  should  touch  the 
arch.)  A  simultaneous  examination  of  the  brick-work  form- 
ing the  upper  portion  of  the  side  walls  should  also  be  made,  as 
it  is  here  that  the  effect  of  the  curving  of  the  buckstaff  from 
too  great  tension,  and  consequent  pressure  against  the  mason- 
work,  is  first  visible. 

The  extreme  limit  of  tension  is  reached  when  the  first 
signs  of  this  appear,  as  nothing  can  be  gained  by  bending  the 
uprights,  and  if  the  latter  are  sufficiently  strong  and  applied 
in  the  numbers  shown  in  the  illustration,  the  arch  may  be  con- 
sidered perfectly  supported.  All  the  rods  should  be  tightened 
to  about  the  same  extent,  although  it  must  be  remembered 
that  the  great  length  of  the  longitudinal  rods  may  prove  decep- 
tive in  estimating  their  tension,  it  being  impossible  to  tighten 
them  to  such  a  degree  as  the  shorter  lateral  ones. 

A  single  additional  precaution  is  recommended,  though  sel- 
dom practiced  by  builders.  This  consists  in  breaking  up  a 
few  thin  roofing  slates  into  fragments  a  couple  of  inches  in 
length,  and  driving  these  with  moderate  force  into  whatever 
crevices  may  still  be  found  in  the  surface  of  the  arch. 

Some  twenty  or  thirty  pails  of  liquid  mud  are  now  poured 
over  the  arch,  and  the  process  repeated  as  it  dries,  until  every 
crack  and  crevice  is  filled,  and  the  roof  rendered  completely 
solid  and  air-tight. 

The  wooden  center  on  which  the  arch  was  built  should 
now  be  removed  by  first  knocking  away  the  little  posts  that 
support  it,  using  a  light  stick  of  timber  as  a  battering-ram,  and 
proceeding  from  one  side  door  to  the  next  until  every  stick 
and  batten  is  removed.  They  should  be  stored  for  future  use. 
Any  indications  of  settling  on  the  part  of  the  arch  must  be 
immediately  counteracted  by  tightening  the  tie-rods;  but 
when  the  precautions  enumerated  have  been  carefully  ob- 
served, this  can  never  occur. 

The  length  of  time  the  completed  furnace  may  now  stand 
untouched  with  advantage  to  the  mason-work  is  only  limited 
.by  the  requirements  of  the  business,  which  almost  invariably 
require  its  being  put  in  commission  at  the  earliest  possible 
moment.  Under  such  circumstances,  a  smoldering  fire  of 
large  logs,  knots,  or  any  slow-burning  waste  material,  should 
10 


146     MODERN"  AMERICAN   METHODS   OF  COPPER  SMELTING. 

at  first  be  kindled  on  the  floor  of  the  ash-pit,  the  grate-bars 
not  being  put  in  place  until  the  masonry  surrounding  the  fire- 
place is  partially  dried. 

In  twelve  or  eighteen  hours,  the  fire  is  elevated  to  its 
proper  place,  and  with  a  nearly  closed  ash-pit  door  and  par- 
tially lowered  damper,  the  process  of  drying  proceeds  gently 
and  without  that  violent  generation  of  steam  and  vapor  that  is 
sure  to  be  accompanied  by  extensive  fissuring  of  the  brick- 
work and  permanent  weakening  of  the  entire  structure. 

A  most  careful  and  repeated  examination  of  the  condition 
of  tie-rods  and  buckstaves  should  be  made  every  twelve  hours 
from  the  first  kindling  of  the  fire  until  the  furnace  has  attained 
its  full  heat,  and  may  be  supposed  to  have  expanded  to  its 
utmost  limits,  although  it  may  be  a  month  or  more  before  all 
evidences  of  movement  cease.  The  first  indication  of  this 
process  will  be  seen  in  the  neighborhood  of  the  bridge  and 
fire-place,  where  the  highest  temperature  prevails.  A  bending  of 
the  buckstaves,  combined  with  a  pressing  in  of  the  skewback  line 
and  an  increased  tension  of  the  cross-rods,  are  warnings  that 
may  soon  be  foUowed  by  either  a  complete  giving  way  of  some 
portion  of  the  iron-work,  or  more  frequently  by  a  bodily  up- 
heaval of  the  arch  and  general  fissuring  of  the  brick-work, 
unless  relieved  by  diminishing  the  strain  to  a  corresponding 
degree.  This  process  of  loosening  must  be  extended  to  the 
entire  iron-work  of  the  furnace,  and  continued  as  long  as  neces- 
sary, the  tension  being  again  increased  if  the  furnace  is  ever 
allowed  to  cool  down  to  any  considerable  degree — an  opera- 
tion more  destructive  to  it  than  many  months  of  ordinary 
wear. 

While  the  apparatus  is  thus  gradually  being  brought  into 
proper  heat,  the  sheet-iron  hopper  should  be  suspended  from 
timbers  resting  upon  the  trussed  beams  of  the  building.  It 
should  be  strongly  constructed  and  well  braced,  and  provided 
with  a  stout  lever,  easily  accessible  to  the  operator  when  stand- 
ing upon  the  floor  of  the  building.  A  track  running  trans- 
versely to  the  row  of  calcining-furnaces,  and  parallel  with  the 
longitudinal  axis  of  the  building,  renders  these  hoppers  easily 
accessible  to  the  car  in  which  each  weighed  charge  of  ore  is 
brought.  The  car  is  provided  with  a  dumping  arrangement, 


CALCINATION  OF  ORE  AND  MATTE.  147 

so  that  it  easily  and  completely  empties  itself  into  the  furnace 
hopper.  The  laborer  who  weighs  and  transports  the  charges 
can  supply  six  furnaces,  provided  everything  is  arranged  as 
herein  described,  or  in  a  similarly  judicious  manner. 

The  outfit  of  tools  may  also  now  be  prepared,  and  should 
consist,  for  each  four-hearth  calciner,  of  6  rabbles,  4  inches  by 
10  inches  and  12  feet  long ;  6  paddles,  8  inches  by  12  inches 
and  12  feet  long ;  4  door-hooks,  to  handle  the  sheet-iron  work- 
ing-door ;  1  long  hooked  and  pointed  iron  poker  for  wood,  or 
an  ordinary  coal  poker,  if  coal  is  used ;  2  ordinary  long-han- 
dled, square-pointed  shovels ;  1  scoop-shovel  (for  coal). 

The  iron  rollers,  usually  employed  as  rests  for  the  long 
tools  at  each  working-door,  soon  lose  their  shape  and  cease  to 
revolve.  It  is  better,  therefore,  to  provide  merely  a  smooth 
iron  bar,  which,  if  kept  well  soaped,  renders  the  handling  of 
the  tools  as  easy  as  any  of  the  more  expensive  devices. 

When  available,  a  free-burning  semi-bituminous  coal  forms 
the  most  economical  fuel  for  calcining  purposes,  but  should 
always  be  burned  upon  a  comparatively  shallow  grate,  instead 
of  using  the  deep  clinker-bed,  so  suitable  to  the  smelting 
process.  At  the  comparatively  low  temperature  suited  to 
calcination,  the  generated  gas  does  not  burn  perfectly,  and  a 
great  waste  of  fuel  occurs.  Coal  should  be  fed  at  short  inter- 
vals— from  30  to  45  minutes — in  quantities  seldom  exceeding 
50  pounds.  When  wood  is  cheap,  nothing  can  excel  it  as  a 
fuel  for  calcining  purposes,  its  long,  hot,  non-reducing  flame 
being  peculiarly  suited  to  the  requirements  of  the  process. 
About  one  and  two-thirds  cords  of  hard,  or  two  cords  of  soft, 
wood  are  commonly  considered  equal  to  2,240  pounds  of  good 
bituminous  coal. 

CONSTRUCTION  OP  FURNACE  STACKS. 

While  the  furnace  is  gradually  getting  into  condition  for  its 
first  charge  of  ore,  an  opportunity  is  offered  to  return  to  the 
question  of  construction  again,  and  describe  a  method  of  build- 
ing stacks  that  is  much  more  economical  than  that  usually  pur- 
sued, and  which,  though  not  new  or  original,  is  certainly  not 
generally  adopted  in  the  erection  of  smelting- works. 

Owing,  perhaps,  to  the  influence  exercised  by  studying  the 


148     MODERN   AMERICAN  METHODS   OF  COPPER   SMELTING. 

practice  of  most  European  builders,  and  by  following  former 
customs  without  thinking  particularly  of  the  possible  oppor- 
tunities for  improvement,  the  vastly  greater  number  of  furnace 
stacks  now  erected  are  very  much  more  costly  than  they  need 
be,  both  as  regards  labor  and  material.  From  a  very  recent 
comparison  of  costs  with  professional  friends,  the  author  has 
found  that  the  average  calciner  stack,  as  erected  by  him  dur- 
ing the  past  twelve  years,  has  cost  less  than  one-half  the 
amount  ordinarily  expended,  making  it  worth  while  to  occupy 
a  few  paragraphs  in  describing  the  more  economical  practice. 

The  most  important  feature  of  a  chimney  is  its  foundation ; 
but  it  is  at  this  very  point  that  a  great  saving  over  ordinary 
practice  may  be  effected  without  lessening  the  stability  of  the 
superstructure. 

A  mere  increase  in  depth  below  the  loose  soil  forming  the 
surface  of  the  ground  does  not  add  in  the  slightest  to  the  value 
of  the  foundation,  after  a  proper  material  for  the  same  has 
once  been  reached  ;  and  as  this  occurs  in  the  greater  number 
of  cases  within  three  or  four  feet  of  the  surface,  the  frequent 
practice  of  additional  excavation  for  the  apparent  purpose  of 
merely  gaining  depth  is  money  thrown  away. 

After  removing  the  loose  surface  soil,  and  penetrating  below 
any  danger  of  frost,  in  the  greater  number  of  cases  no  advan- 
tage would  be  gained  by  excavating  to  a  depth  of  50  feet,  unless 
solid  bed-rock  were  reached. 

Any  kind  of  gravel,  hard-pan,  or  even  soft  loam  or  sand,  if 
homogeneous,  will  answer  the  purpose  perfectly,  it  being  under- 
stood that  reference  is  here  made  to  an  ordinary  calciner  or 
smelter  stack  not  exceeding  80  feet  in  height. 

In  the  case  of  a  yielding  sand  bottom,  and  especially  if  the 
line  of  division  between  two  strata  of  varying  quality  happens 
to  cross  the  excavation,  it  is  well  to  form  a  solid  floor  to  the 
pit  by  putting  in  a  double  layer  of  three-inch  plank,  nailed  cross- 
wise. But  in  all  ordinary  cases  the  hole  should  be  simply  filled 
with  broken  stone,  about  the  size  of  ordinary  road  metal  This 
material,  when  well  rammed  into  place  and  thoroughly  grouted, 
by  pouring  in  a  sufficient  quantity  of  mortar  composed  of  one 
part  each  of  lime  and  cement,  and  three  of  sand,  makes  a 
foundation  infinitely  superior  to  one  formed  of  a  few  large 


CALCINATION   OF  OKE   AND  MATTE.  149 

stones,  the  slightest  settling  of  any  one  of  which  will  throw  the 
chimney  out  of  perpendicular. 

The  excavation  should  be  at  least  two  feet  larger  in  every 
direction  than  the  base  of  the  chimney,  and  the  stone-work  of 
the  latter,  laid  in  lime  and  cement,  should  begin  some  three 
feet  below  the  surface,  at  which  point  the  brick-work  usually 
begins. 

If  a  cupola  sm  el  ting-furnace  is  in  operation  in  the  immedi- 
ate vicinity,  nothing  can  be  more  satisfactory  or  economical 
than  the  following  plan,  pursued  by  the  author  on  several  oc- 
casions : 

An  excavation  being  made  of  the  usual  size,  the  molten 
slag  from  the  smelting-furnace  is  wheeled  to  the  spot  in  the 
usual  movable  slag-pots,  and  poured  at  once  into  the  hole, 
which,  when  filled  to  the  proper  height  with  the  fused  rock, 
and  leveled  by  means  of  little  clay  dams  along  the  edges,  so  as 
to  present  a  smooth  surface  for  the  masons  to  begin  on,  will 
contain  a  solid  block  of  lava,  weighing  many  tons,  and  as  im- 
movable as  a  ledge  of  rock. 

In  constructing  a  stack,  we  have  to  determine  the  size  of 
flue  desired,  and  intimately  connected  with  the  same  is  the  de- 
gree of  latter,  or  taper,  which  shall  be  given  to  the  structure. 

The  object  of  this  latter  is  two-fold  :  1st.  For  appearance. 
2d.  For  the  sake  of  strength.  The  first  reason  may  be  entirely 
neglected  in  metallurgical  architecture,  and  experience  has 
shown  that,  within  the  limit  of  height  mentioned,  a  batter  of 
one-eighth  of  an  inch  to  the  foot  is  ample.  Nor  need  the  taper 
be  begun  until  the  stack  rises  above  the  roof,  as  that  portion  of 
the  structure  within  the  building  is  amply  protected  from  the 
force  of  the  wind. 

By  thus  decreasing  the  amount  of  taper,  we  greatly  increase 
the  capacity  of  the  stack,  as  experience  shows  that  a  contrac- 
tion of  the  flue  in  its  upper  portion  is  accompanied  with  a  cor- 
responding diminution  of  draught,  while  a  positive  enlarge- 
ment of  the  same  toward  the  top  has  a  most  beneficial  influ- 
ence. This  latter  point  is  gained  by  lessening  the  thickness 
of  the  chimney  walls  as  they  grow  higher,  while  the  outside 
taper  remains  constant. 

All  calculations   and  formulae    regarding    the    necessary 


150     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

size  of  any  flue  for  a  given  duty  have  been  found  so  greatly 
modified  by  circumstances — such  as  variations  of  internal  and 
external  temperature ;  humidity  of  atmosphere  and  state  of 
barometer ;  change  of  winds,  etc. — that  it  is  found  safest  to 
rely  upon  experience  and  analogy ;  and  after  beginning  with  a 
much  larger  flue  for  safety,  the  author  has  finally  found  a  stack 
42  inches  square  inside,  at  its  narrowest  part,  and  65  feet  high, 
to  possess  ample  capacity  for  two  large  calcining-furnaces  such 
as  just  described.  It  is  proper  to  add  that  a  much  smaller 
stack  will  produce  the  draught  usually  considered  as  quite 
sufficient  for  the  calcining  process  ;  but  long-continued  experi- 
ment has  shown  such  extraordinarily  favorable  results,  as 
regards  both  capacity  and  perfection  of  roast,  to  arise  from 
greatly  increasing  the  ordinary  calciner  draught,  that  a  sharp 
and  powerful  draught  appears  as  essential  to  a  calciner  as 
to  a  smelting-furnace. 

For  this  reason,  also,  no  more  than  two  furnaces  should  be 
led  into  a  common  stack,  it  being  almost  impossible  properly 
to  equalize  the  admission  of  air  to  each  calciner,  and  to  pro- 
duce that  sharp  and  vigorous  draught  so  essential  to  rapid 
oxidation,  and  especially  to  the  conveyance  of  the  sheet  of 
flame  and  heated  gases  over  the  whole  length  of  a  4-hearth 
calcining-furnace.  The  interposition  of  dust-chambers,  or  pref- 
erably of  large  flues,  filled  with  parallel  rows  of  sheet-iron, 
according  to  the  method  found  so  efficient  and  economical  at 
Ems,' is  of  course  necessary,  and  should  be  present  in  any 
case.*  Limited  experiments  conducted  by  the  author  fully 
satisfy  him  of  the  great  benefit  to  be  derived  from  the  adop- 
tion of  this  economical  and  efficient  method  of  condensation. 

The  size  of  chimney  mentioned — 42  inches — will  answer  for 
all  elevations  up  to  5,000  feet  above  sea-level.  For  each  1,000 
additional  height,  these  figures  should  be  increased  one  half- 
inch. 

For  a  calciner  chimney  of  this  size  and  65  feet  in  height, 
the  walls  at  the  base  should  be  IT  inches  thick,  the  length  of 
two  red  brick,  no  fire-brick  being  needed,  as  the  gases  are 


*  See  description  of  Ems  method  of  condensation,  by  Professor  Egleston, 
in  Transactions  of  the  American  Institute  of  Mining  Engineers. 


CALCINATION  OF  OEE  AND  MATTE.  151 

sufficiently  cooled  by  their  passage  through  the  loog  furnace 
and  flue.  This  thickness  is  maintained  for  a  height  of  25  feet 
from  the  ground,  which  brings  it  somewhat  above  the  roof  of 
the  building.  At  this  point,  the  external  batter  of  one-eighth 
of  an  inch  to  the  foot  is  begun,  and  an  internal  set-off  of  4 
inches  is  taken  ;  thus  decreasing  the  thickness  of  the  walls  to 
13  inches,  and  enlarging  the  flue  to  50  inches. 

This  constant  taper  is  maintained  by  the  employment  of 
an  ordinary  beveled  plumb-bob,  which  obviates  any  trouble  or 
calculation.  This  condition  of  affairs  is  continued  for  another 
25  feet,  during  which  distance  the  flue  is  contracted  to  a  size 
of  about  44  inches,  when  another  internal  4-inch  set-off  is 
taken,  increasing  the  same  to  52  inches,  while  the  walls  are 
diminished  to  8  inches. 

This  being  continued  for  15  feet,  gives  the  full  height  of 
65  feet,  the  flue  at  the  top  being  still  48  inches  square,  or  6 
inches  larger  than  at  the  base.  No  ornamental  finish  at  the 
top  should  ever  be  allowed,  the  stack  either  being  surmounted 
by  a  light  casting  to  hold  the  brick  in  place,  or  left  without 
this  protection,  the  iron  braces  being  usually  sufficient  to  pre- 
vent the  loosening  of  the  upper  rows  of  brick- work.  An  orna- 
mental cap  is  simply  a  source  of  annoyance  and  danger,  and 
should  never  be  permitted  in  a  stack  devoted  to  the  passage 
of  sulphurous  vapors. 

A  chimney  of  this  size  is  best  built  from  the  outside,  a 
scaffold  being  erected  by  placing  eight  stout  poles  about  the 
base  of  the  proposed  structure,  nailing  cross-pieces  at  the 
proper  height  for  the  plank  staging,  and  thoroughly  bracing 
the  uprights  by  boards  nailed  diagonally  from  one  to  the  other. 

The  uprights  may  be  lengthened  out  almost  indefinitely 
by  careful  splicing,  and  as  the  stack  grows  higher,  new  cross- 
pieces  are  spiked  every  five  feet,  and  men  and  material  thus 
maintained  at  the  desired  elevation.  A  rope  and  bucket,  with 
a  single  wooden  block  fastened  to  the  railing  of  the  staging, 
and  manipulated  principally  from  the  ground  level,  forms  the 
most  economical  means  of  elevating  the  requisite  material, 
while  a  single  laborer  above  is  able  to  furnish  four  masons 
with  brick  and  mortar,  most  of  the  work  being  done  from  be- 
low. It  is  best  to  employ  four  masons,  so  that  one  can  work 


152      MODEEN  AMERICAN   METHODS   OF  COFFEE  SMELTING. 

on  each  wall  of  the  stack,  and  their  position  should  be  changed 
twice  daily,  in  order  to  equalize  any  differences  in  the  amount 
of  mortar  used,  etc. 

Like  all  other  mason-work  that  is  to  be  exposed  to  heated 
sulphurous  gases,  the  interior  portion  of  the  stack  must  be  laid 
in  clay  mortar  (ordinary  sticky  mud) ;  while  the  remainder  of 
the  structure  should  be  laid  in  lime  mortar,  on  account  of  its 
superior  tenacity.  To  prevent  the  penetration  of  the  vapors 
into  the  porous  brick,  the  interior  of  the  flue  should  be  tho- 
roughly plastered  with  clay  throughout  its  entire  extent. 

While  the  durability  of  a  chimney  of  this  description  is 
largely  dependent  upon  its  being  ironed,  it  is  still  more  de- 
pendent upon  its  not  being  ironed  too  stiffly.  A  stack  with 
corners  thoroughly  inclosed  in  stiff  angle  iron,  tightly  held 
together  with  frequent  braces,  will  fissure  and  give  out  in  a 
few  years,  while  a  similarly  built  chimney  containing  a  few 
light  irons  merely  to  hold  the  brick-work  in  place,  will  last 
from  twenty  to  forty  years. 

This  is  the  result  of  personal  experience,  confirmed  by  the 
observations  of  most  other  constructing  engineers,  and  is  es- 
pecially the  case  in  countries  where  high  winds  and  violent 
fluctuations  of  temperature  are  prevalent. 

Eight  uprights  of  f-inch  by  f-inch  iron,  each  upright  being 
placed  about  4  inches  from  each  corner  of  the  stack,  and  pass- 
ing through  rectangular  openings  cut  in  J  by  2-inch  flat  iron, 
which  latter  pieces  are  laid  in  the  brick-work  from  30  to  36 
inches  apart,  are  amply  sufficient  for  the  purpose.  The  holes 
must  be  so  punched  that  the  uprights  can  be  wedged  tightly 
against  the  brick- work,  which  is  thus  held  in  place  even  after 
the  mortar  has  long  succumbed  to  the  combined  influence  of 
the  roast  gases  and  the  elements.  As  a  striking  example  of 
the  accuracy  of  the  above  remarks,  the  reverberatory  smelter 
stacks  of  the  Detroit  Smelting  Company's  copper  refining  fur- 
naces at  Lake  Superior  may  be  mentioned,  where,  on  building  a 
strongly  ironed  stack,  they  found  it  fissure  and  become  unsound 
in  a  very  short  time ;  whereas  their  ordinary  stacks,  anchored 
only  by  means  of  occasional  straps  of  flat  iron  built  into  the 
chimney  walls  and  bent  over  at  each  end,  stand  for  fifteen 
years  or  more  without  showing  crack  or  imperfection. 


CALCINATION   OF  ORE   AND  MATTE.  153 

A  row  of  headers  should  be  introduced  at  about  every 
eighth  course,  and  the  lower  portion  of  the  stack  into  which 
the  two  calciner  flues  enter  on  opposite  sides  should  be  divided 
by  a  4-inch  partition  wall  into  two  equal  compartments.  This 
wall,  extending  some  five  feet  above  the  entrance  flues,  serves 
to  bend  each  current  in  an  upward  direction,  and  thus  prevent 
the  whirl  and  disturbance  of  draught  resulting  from  the  meet- 
ing of  two  opposing  currents. 

The  following  interesting  observation  has  been  communi- 
cated by  Messrs.  Cooper  and  Patch,  superintendent  and  chem- 
ist of  the  Detroit  Refining- Works  : 

In  most  reverberatory  furnaces,  the  flue  enters  the  stack 
at  some  distance  above  its  base,  and  consequently  there  is  a 
cavity  inclosed  by  the  chimney  walls,  of  greater  or  less  depth 
below  the  embouchure  of  the  flue.  When  this  apparently  use- 
less cavity  has  become  filled  up  from  the  falling  in  of  the  stack 
lining,  drippings  from  the  molten  brick,  or  other  causes,  the 
draught  at  once  suffers  and  the  capacity  of  the  furnace  is 
greatly  diminished. 

Whether  this  phenomenon  arises  from  the  loss  of  the  elastic 
air-cushion  that  is  normally  present,  or  whether  there  is  some 
other  reason,  the  fact  remains,  and  although  the  observations 
have  been  confined  mostly  to  smelting-f  urn  aces,  it  is  probable 
that  a  calcining-furnace  may  be  affected  in  a  similar  manner, 
and  therefore  in  all  cases  where  a  horizontal  or  inclined  flue 
enters  a  stack,  it  should  be  so  constructed  as  to  leave  an  open 
space  of  from  4  to  6  feet  below  it.  This  need  not  communi- 
cate with  the  outside  air  in  any  way,  except  for  the  purpose  of 
cleaning  the  stack  or  entering  it  for  repairs. 

It  is  well  to  provide  every  high  stack  with  a  good  lightning- 
rod,  properly  fastened  and  insulated. 

The  building  that  covers  any  considerable  number  of  cal- 
cining-f urn  aces  is  necessarily  of  great  extent,  and  should,  if 
possible,  be  built  of  very  light  and,  at  the  same  time,  fire-proof 
materials. 

Scarcely  anything  fills  these  requirements  so  thoroughly  as 
a  medium  grade  of  corrugated  iron.  This,  if  well  fastened 
down,  and  painted  every  three  or  four  years,  will  be  found  the 
most  economical  and  satisfactory  material  for  both  sides  and 


151     MODERN"  AMERICAN  METHODS   OF   COPPER  SMELTING. 

roof  that  is  yet  known.  If  the  number  of  furnaces  under  a 
single  roof  exceeds  two,  they  should  be  placed  at  right  angles 
to  the  greatest  length  of  the  building,  a  space  of  only  three  feet 
being  left  between  the  rear  end  of  the  furnace  and  the  corre- 
sponding side  of  the  building,  while  between  the  fire-box  and 
the  lower  side  of  the  building  there  should  be  ample  room  for 
a  drive-way  for  the  conveyance  of  fuel,  as  well  as  for  a  railroad 
parallel  to  the  same  and  close  to  the  wall,  over  which  the  cal- 
cined ore  may  conveniently  be  dumped  into  a  paved  and 
roofed  inclosure  on  a  level  as  low  as  the  circumstances  of  the 
case  permit.  The  sixteen-foot  calciners-  should  be  separated 
by  spaces  of  at  least  fourteen  feet. 

As  the  main  building  for  these  long  calcining-furnaces  must 
be  from  eighty  to  ninety  feet  in  width,  it  is  often  the  practice 
to  support  the  cross-beams  on  posts  that,  if  properly  placed 
close  to  the  furnace  and  midway  between  the  working  openings, 
need  not  interfere  with  the  long  tools  in  use.  But  there  is  no 
difficulty  an  constructing  trusses  to  support  a  roof  of  this  size 
without  the  aid  of  posts,  nor  need  the  expense  be  much  greater. 
The  principal  difficulty  is  encountered  in  raising  these  im- 
mensely long  and  heavy  "  bents  ; "  but  this  may  be  entirely 
obviated  by  constructing  a  series  of  cheap  scaffoldings,  and 
putting  them  together  piece  by  piece,  instead  of  attempting  to 
raise  the  entire  "  bent"  bodily.  The  ridge  of  the  roof  should 
be  surmounted  by  a  continuous  ventilator  throughout  its  entire 
extent.  The  details  of  this  work  may  be  intrusted  to  any  ex- 
perienced carpenter. 

COST  OF  CONSTBUCTION  OF  CALCINING-FURNACE. 

The  following  estimates  of  cost  are  taken  from  notes  that 
cover  the  construction  of  a  considerable  number  of  large  cal- 
cining-furnaces, and  being  given  without  alteration  or  omis- 
sions, excepting  the  necessary  reduction  to  our  assumed  stand- 
ard of  costs,  should  furnish  reliable  figures  on  which  to  base 
future  plans  : 


CALCINATION  OF  ORE  AND  MATTE.  155 

COST  OP  ONE  FOUK-HEARTH  CALCINEB. 

Excavation — 45  days  at  $1.50 $67.50 

Removal  of  material  excavated 35.00 

Superintendence  and  miscellaneous 24.00     $126.50 

Foundation  Walls— 1,840  cubic  feet. 

2,000  slag-brick  at  2  cents 40.00 

20  days  stone-mason  and  helpers 120.00 

Materials  for  mortar 28.00 

Labor  on  same  and  utensils 16.00 

Miscellaneous  labor 12.00 

Superintendence 15.00     $231.00 

Brick-work  on  Furnace  Proper. 

2,420  cubic  feet,  say  50,000  red  brick  at  $8 $400.00 

7,500  fire-brick  at  $40 300.00 

Lime  and  sand 137.00 

4  tons  fire-clay  at  $8 32.00 

8i  tons  brick-clay  at  $1 12.00 

32  loads  sand  at  $1.50 48.00 

112  days  brick-masons'  labor  at  $4 448, 00 

112  days'  ordinary  labor  at  $1.50 168.00 

3  days  carpenters'  labor  $3 9.00 

Miscellaneous  labor 35.00 

8  days,  blacksmith  and  helper 40.00 

Materials  consumed  by  same 8.00 

Superintendence 112.00  $1,749.00 

Iron  Work. 
66  buckstaves  (old  rails),  6£  feet  long,  80  pounds,  at  % 

cent  per  yard $85.80 

Tie-rods  and  loops,  2, 056  feet,  1^-inch  round  iron  =  8,327 

pounds,  at  2  cents 166 . 54 

Flat  iron  for  skewback,  grates,  etc.  —  2,064  pounds,  at  2 

cents ; 41 .28 

16  cast  frames  and  doors,  at   156  pounds  each  —  2,496 

pounds,  at  2}  cents 62.40 

Fire-doors  and  other  small  castings 16 . 50  $372 . 52 

Nuts  and  bolts 6 . 25 

Short  flue,  with  damper  and  £  cost  of  stack 364.00 

Grading  and  miscellaneous 47.50 

Tracks  for  feed  and  discharge  of  ore 62.40 

Set  tools,  complete,  as  per  former  schedule,  1,250  pounds, 

at  2  cents 25  00 

Labor  on  same , 18 . 00 

One  iron  ore  car  (list  price) 85.00 


Grand  total $3,130.17 

The  repairs  on  a  thoroughly  built  calciner  should  be  noth- 
ing for  the  first  three  years ;  for  the  succeeding  seven  years, 


156      MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

they  will  average  3  per  cent,  per  annum  on  its  first  cost,  while 
from  its  tenth  to  its  fifteenth  year,  5  per  cent,  per  annum  will 
probably  be  expended  in  renewing  the  hearth  and  roof  once 
and  patching  the  furnace  in  various  places. 

After  fifteen  years  of  constant  usage,  ifc  is  cheaper  to  build 
anew  furnace  than  to  keep  the  old  one  in  repair ;  but  few 
metallurgical  enterprises  in  this  country  require  to  provide  for 
a  period  longer  than  the  above. 

The  variety  of  reverberatory  calciner  known  as  the  muffle 
furnace  is  now  seldom  used  by  the  copper  smelter,  as,  except 
for  purposes  of  acid  manufacture,  it  possesses  few  advantages 
above  the  ordinary  hearth  variety,  and  in  case  this  branch  of 
metallurgy  is  also  practiced,  some  of  the  newer  forms  of  auto- 
matic furnaces  have  displaced  the  muffle.  The  high  cost  of 
construction  and  greater  consumption  of  fuel  are  also  adverse 
to  its  employment,  and  although,  from  its  gentle  and  regular 
heat,  it  possesses  decided  advantages  in  the  treatment  of  easily 
fusible  substances,  it  is  rather  suited  to  the  calcination  of 
matter  containing  much  lead,  or  of  pyrites  with  salt,  as  in 
the  Henderson  process,  none  of  which  operations  come  within 
the  scope  of  this  treatise. 

An  easily  fusible  ore  can  be  very  efficiently  protected  from 
the  fierce  heat  of  the  first  hearth  of  an  ordinary  calciner  by 
the  construction  of  a  four-inch  curtain  arch,  covering  one  third 
or  more  of  its  surface  from  the  fire-bridge  onward,  though 
such  a  precaution  is  seldom  necessary,  excepting  in  the  case  of 
matte  calcination,  which  requires  but  slight  modifications  of 
the  roasting  process  as  applied  to  ordinary  sulphide  ores. 

The  process  of  ore  calcination,  like  most  other  operations 
based  on  chemical  reactions,  must  be  understood  before  it  can 
be  properly  and  intelligently  executed,  and  no  description  of 
the  same  would  be  complete  without  a  brief  review  of  the 
chemistry  of  the  calcining  process. 


CHAPTEK  VIII. 

THE   CHEMISTRY   OF  THE  CALCINING  PEOCESS. 

A  SUFFICIENT  idea  of  the  chemical  reactions  that  occur  in  this 
important  metallurgical  process  may  be  obtained  by  following 
an  ordinary  pyritous  ore  in  its  passage  through  the  roasting- 
f urn  ace,  and  carefully  noting  all  the  changes  that  it  undergoes 
from  the  moment  of  its  introduction  until  it  is  ready  for  the 
succeeding  fusion  ;  nor  are  the  conditions  in  either  roast-heaps 
or  stalls  so  different  as  to  require  any  separate  consideration. 

A  typical  ore  for  this  purpose  might  consist  of  a  large  pro- 
portion of  pyrite,  say  45  per  cent.,  some  20  per  cent,  of  chal- 
copyrite  (containing  about  one  third  copper),  with  a  slight  ad- 
mixture of  zincblende,  galena,  and  sulphide  of  silver,  while  the 
remainder  of  the  ore  would  usually  'consist  of  quartz  or  sili- 
ceous material,  which  may  be  regarded  as  practically  inert  in 
its  effect  upon  the  process  of  calcination.  A  charge  of  such 
ore,  being  introduced  upon  the  hearth  of  a  roas ting-furnace 
still  at  a  bright  red  heat  from  the  preceding  operation,  exerts 
a  powerfully  cooling  influence  upon  the  glowing  brick-work, 
and  within  ten  or  fifteen  minutes  reduces  the  temperature  to  a 
point  below  the  ignition-point  of  sulphur,  the  ore  at  the  same 
time  giving  off  its  moisture,  and  gaining  so  much  heat  that  a 
very  slight  aid  from  the  fuel  on  the  grate  is  sufficient  to  start 
the  oxidation  of  the  iron  pyrites,  as  shown  by  the  blue  flicker- 
ing flame  that  plays  over  the  surface  of  the  charge,  beginning 
at  that  portion  of  the  same  that  borders  on  the  already  hot 
charge  occupying  the  adjoining  hearth,  and  gradually  advanc- 
ing toward  the  rear,  until  every  spare  inch  of  surface  is  in  a 
state  of  active  combustion.  The  rapidity  of  this  process  of 
oxidation  varies  according  to  the  degree  of  temperature  and  the 
sharpness  of  the  draught,  but  should  not  occupy  more  than  an 
hour  from  the  first  introduction  of  the  charge.  The  compo- 
sition of  iron  pyrites  (FeS2)  is  such  that  while  one  atom  of  sul- 


158      MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

phur  is  united  to  the  iron  with  considerable  tenacity,  the 
second  atom  is  held  by  very  feeble  bonds  ;  and  becoming  vola- 
tile at  the  moderate  temperature  of  the  calcining-furnace,  unites 
with  the  oxygen  of  the  air,  forming  sulphurous  acid  (SO2), 
which  escapes  in  the  form  of  an  invisible  gas.  This  reaction  is 
accompanied  by  a  very  considerable  evolution  of  heat  and  the 
flickering  blue  flame  already  mentioned.  Being  entirely  de- 
pendent upon  the  oxygen  derived  from  the  air,  this  reaction  is 
confined  principally  to  the  surface  of  the  charge,  which,  if  left 
undisturbed,  would  soon  undergo  a  slight  fusion,  causing  a 
caking  of  the  ore,  and  still  further  hindering  the  extension  of 
the  process.  It  is  therefore  just  at  this  point  that  the  necessity 
for  frequent  and  vigorous  stirring  becomes  strikingly  apparent. 
By  this  manipulation,  any  incipient  crust  that  may  have  formed 
is  broken  up,  the  temperature  of  the  layer  of  ore  is  equalized 
throughout  its  entire  depth,  and  fresh  particles  of  ore  are  con- 
stantly exposed  to  the  influence  of  the  air. 

The  stirring  should  begin  on  the  first  appearance  of  the  blue 
flame,  and  continue  for  ten  minutes  at  a  time,  with  equal  in- 
tervals of  rest,  during  which  time  the  working  openings  should 
be  closed,  while  an  ample  air  supply  is  admitted  through  the 
regular  channels  provided  for  this  purpose.  The  stirring  should 
take  place  from  both  sides  of  the  furnace  at  the  same  time,  and 
should  be  systematic,  vigorous,  and  thorough  ;  extending  to  the 
very  bottom  of  the  charge,  and  omitting  no  portion  of  the 
ore. 

During  this  period  of  roasting,  and  until  the  disappearance 
of  the  blue  flame,  the  roast  gases  consist  almost  exclusively 
of  sulphurous  acid,  together  with  steam  from  the  moisture 
present,  and  the  invariable  products  of  the  combustion  of  the 
fuel. 

It  will,  of  coarse,  be  understood  that  the  SO2  and  other 
roast  gases  form  but  a  small  proportion — seldom  more  than  2 
per  cent. — of  the  air  issuing  from  a  calciner  stack ;  atmos- 
pheric air  always  being  present  in  overwhelming  proportions. 
The  SO2  results  from  the  direct  oxidation  of  one  atom  of  the 
sulphur  contents  of  the  iron  pyrites,  or,  when  the  temperature 
is  somewhat  high,  of  the  absolute  volatilization  of  this  atom  of 
sulphur  as  sulphur,  and  its  immediate  combustion  to  SO2. 


THE   CHEMISTRY   OF  THE   CALCINING  PEOCESS.  159 

The  next  stage  of  the  process  may  be  reckoned  from  the 
beginning  of  the  oxidation  of  the  iron  of  the  pyrites,  and  also 
of  its  second  atom  of  sulphur.  This  is  a  much  less  rapid  and 
vigorous  process  than  the  preceding,  and  is  attended  by  the 
formation  of  a  certain  amount  of  sulphuric  acid,  in  addition  to 
the  sulphurous  acid,  which  is  still  generated  in  large  quanti- 
ties. The  means  by  which  the  former  acid  was  produced  was 
not  clearly  understood  until  Plattner's  patient  and  ingenious 
researches  developed  the  "  contact  theory,"  according  to  which, 
sulphurous  acid  and  the  oxygen  of  the  air,  in  the  presence  of 
large  quantities  of  heated  quartz,  or  other  neutral  material, 
combine  to  form  sulphuric  acid,  which  may  escape  invisible,  or 
in  the  form  of  white  vapors  when  hydrated,  or  may  in  the 
instant  of  its  formation  combine  with  any  strong  base  that  may 
be  present. 

In  the  case  under  consideration,  protoxide  of  iron  (FeO), 
arising  perhaps  from  the  very  particle  of  pyrites  whose  oxida- 
tion gave  rise  to  the  sulphuric  acid,  is  at  hand ;  and  while  the 
greater  proportion  of  the  sulphuric  acid  formed  escapes  into 
the  atmosphere,  a  certain  amount  combines  with  the  protoxide 
of  iron  to  form  ferrous  sulphate,  whose  presence  may  easily  be 
detected,  owing  to  its  solubility  in  water. 

From  the  very  commencement  of  the  formation  of  sulphuric 
acid,  a  new  and  powerful  oxidizing  agent  is  gained,  as  the  proto- 
sulphate  of  iron  is  easily  broken  up  by  heat.  The  decompo- 
sition of  its  acid  into  S02  and  O  promotes  the  oxidation  of  other 
sulphides  present  to  sulphates,  while  the  protoxide  of  iron  is 
raised  to  the  sesquioxide  of  that  metal — a  tolerably  stable 
compound,  and  one  usually  found  in  large  quantities  in  thor- 
oughly roasted  pyritic  ores.  Before  the  complete  decomposi- 
tion of  the  ferrous  sulphate  has  occurred,  and  indeed  while 
some  considerable  proportion  of  sulphide  of  iron  may  yet  re- 
main, an  analogous  process  takes  place  with  the  chalcopyrite, 
its  ferruginous  portion  following  almost  precisely  the  same 
course  as  the  iron  pyrites,  while  its  copper  contents  are  trans- 
formed into  cupric  sulphate,  which,  on  the  addition  of  water, 
becomes  copper  vitriol,  easily  recognized  by  its  color  and  by 
several  simple  and  well-known  tests. 

As  the  process  continues,  and  the  temperature  is  gradually 


160      MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

raised,  this  salt  also  undergoes  decomposition,  yielding  at  first 
a  basic  sulphate  of  copper,  which,  upon  losing  its  acid,  becomes 
a  dioxide  and  eventually  a  protoxide  of  that  metal.  These  last 
changes,  however,  require  a  protracted  high  temperature. 

The  oxidation  of  the  iron  present  is  pretty  well  advanced  at 
the  time  of  the  maximum  formation  of  cupric  sulphate ;  but  it 
is  not  until  the  decomposition  of  at  least  75  per  cent,  of  the 
last-named  salt  that  the  formation  of  sulphate  of  silver  begins 
with  any  considerably  energy.  When  once  fairly  started,  how- 
ever, this  interesting  and  important  reaction  progresses  with 
great  rapidity,  and  the  decomposition  of  the  comparatively 
large  proportion  of  sulphate  of  copper  present  furnishes  ample 
oxidizing  influence  for  the  minute  quantities  of  sulphide  of 
silver.  The  maximum  formation  of  the  latter  substance  usually 
coincides  with  the  almost  entire  destruction  of  the  former  salt, 
and  it  is  at  this  point  that  the  Ziervogel  calcination  should 
terminate,  as  any  further  exposure  of  the  silver  salt  to  heat 
lessens  its  solubility  in  water,  and  may  even  threaten  its  exist- 
ence. The  complete  decomposition  of  the  argentic  sulphate  is 
only  accomplished  by  a  long  exposure  to  a  high  temperature, 
which  is  now  easily  borne  by  most  ores  and  mattes,  the  easily 
melted  sulphides  having  been  converted  into  almost  infusible 
oxides  and  basic  sulphates. 

Galena  (sulphide  of  lead),  when  present,  is  converted  almost 
entirely  into  a  sulphate  of  that  metal,  which,  by  a  higher  tem- 
perature, is  partially  decomposed  with  the  evolution  of  sul- 
phurous acid  and  the  final  production  of  a  mixture  of  free 
oxide  of  lead  with  sulphate,  the  proportions  of  these  two  sub- 
stances varying  according  to  the  quantity  of  foreign  sulphides 
present. 

Zincblende  requires  a  higher  heat  for  its  thorough  oxida- 
tion than  any  of  the  preceding  sulphides,  but  with  care  may 
be  eventually  changed  into,  an  oxide,  although  a  certain  amount 
of  basic  sulphate  of  zinc  nearly  always  remains.  This  includes 
all  the  sulphides  assumed  to  have  been  present  in  the  ore 
under  consideration,  nor  will  others  be  encountered  in  practice 
unless  under  very  exceptional  circumstances.  Sulphide  of 
manganese  is  an  occasional  unimportant  constituent  of  mattes, 
and  presents  no  particular  difficulty  in  calcining,  being  easily 


THE   CHEMISTRY   OF  THE   CALCINING  PROCESS.  161 

oxidized  to  a.  basic  sulphate,  insoluble  in  water,  which  is  stable 
except  at  the  highest  roasting  temperatures,  when  it  yields  up 
its  acid  in  the  shape  of  SO2,  and  remains  as  a  mixture  of  man- 
ganous  and  manganic  oxides.* 

The  gangue-rock  of  copper  ores,  being  usually  siliceous, 
undergoes  no  change  and  exerts  no  influence  upon  the  calcin- 
ing process,  except  in  so  far  as  it  assists  in  the  oxidation  of 
sulphurous  to  sulphuric  acid  by  contact,  as  already  mentioned. 

Calc-spar  loses  its  carbonic  acid  and  is  converted  into  gyp- 
sum (calcium  sulphate),  while  heavy-spar — sulphate  of  baryta 
— undergoes  no  change,  except  in  the  presence  of  a  powerful 
reducing  atmosphere  and  at  a  high  temperature,  when  it  may 
be  changed  into  sulphide  of  barium.  This  is  soluble  in  water, 
and  it  has  been  suggested  to  use  its  solubility  to  remove  it 
when  its  presence  is  particularly  objectionable.  A  number  of 
trials  in  this  direction  were  made  by  the  author  in  1872  on  the 
heavy-spar  ores  of  Mount  Lincoln,  Colorado,  with  very  poor 
results ;  as  it  was  found  extremely  difficult  to"  reduce  the 
barium  sulphate  to  sulphide  without  mixing  an  amount  of  coal- 
dust  with  the  ore  at  least  equal  to  the  weight  of  the  heavy-spar 
present — from  30  to  40  per  cent. — while  the  BaS  formed  at 
this  high  temperature  is  only  partially  soluble  in  water. 

Arsenic  and  antimony,  when  present,  are  usually  combined 
with  some  metallic  base,  and  behave  like  sulphur  to  a  certain 
extent ;  but  they  give  off  a  much  smaller  proportion  as  vola- 
tile antimonious  and  arsenious  acids,  while  they  combine  to 
a  much  greater  extent  with  the  metallic  bases,  forming  salts 
difficult  to  decompose  and  extremely  injurious  to  the  quality 
of  the  copper. 

Under  such  circumstances,  the  roasting  should  be  contin- 
ued in  the  usual  manner  until  all  the  sulphides  present  are 
oxidized  and  the  resulting  sulphates  for  the  most  part  decom- 
posed. At  this  stage,  from  4  to  6  per  cent,  of  charcoal  dust 
or  fine  bituminous  or  anthracite  coal-screenings  should  be 

*  This  reaction  of  MnS  is  given  in  a  small  pamphlet  devoted  to  the  study 
of  the  reactions  that  take  place  in  roasting  the  Mansfeld  copper  matte  for 
the  extraction  of  silver  by  the  Ziervogel  method;  but  it  is  impossible  to 
credit  any  individual  authorities  with  the  statements  made  in  the  preceding 
few  paragraphs,  they  being  for  the  most  part  matters  of  general  information. 
11 


162      MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

thrown  upon  the  charge  and  thoroughly  incorporated  with  it 
by  vigorous  stirring,  the  heat  at  the  same  time  being  raised  to 
the  highest  practicable  limits.  The  antimonates  and  arsenates 
of  iron  and  copper  are  rapidly  reduced  by  this  means,  and  a 
considerable  proportion .  of  the  injurious  metalloids  are  vola- 
tilized, much  to  the  benefit  of  the  resulting  copper.  The  charge 
should  remain  in  the  furnace  until  all  the  incorporated  carbon 
is  consumed. 

In  the  foregoing  description,  the  process  of  calcination  has 
been  carried  much  farther  than  is  generally  needed,  or  even 
desired,  in  an  ordinary  oxidizing-roasting  as  a  preliminary  to 
fusion. 

Sufficient  sulphur  must  always  be  present  in  the  smelting 
mixture  to  prevent  the  formation  of  too  rich  a  matte,  which 
entails  heavy  losses  in  metal  and  other  injurious  consequences. 
But  it  is  not  a  simple  matter  to  determine  in  advance  exactly 
the  amount  of  sulphur  necessary  to  produce  a  matte  of  any 
given  grade.  This  depends  not  only  upon  the  character  of 
the  furnace  process  to  be  employed — that  is,  whether  blast  or 
reverberatory — but  also  to  a  considerable  extent  upon  the 
manner  in  which  the  residual  sulphur  is  combined  with  the 
bases  present ;  upon  the  rapidity  of  the  fusion ;  the  quality  of 
the  fuel ;  the  volume  and  pressure  of  the  blast ;  character  of 
the  gangue  and  flux  ;  and  numerous  other  factors.  Whatever 
may  be  the  condition  of  affairs,  however,  it  may  be  pretty 
safely  predicted  that  the  percentage  of  the  resulting  matte  in 
copper  will  almost  invariably  be  very  considerably  lower  than 
is  either  expected  or  desired,  so  that  there  is  little  danger  that 
the  calcining  department  of  any  newly  constructed  plant  will 
have  too  great  a  capacity  in  proportion  to  the  rest  of  the 
establishment,  and  many  serious  errors  and  disappointments 
can  be  traced  directly  to  this  habit  of  overestimating  the  prob- 
able quality  of  the  matte  and  failing  to  provide  sufficient  cal- 
cining appliances. 

In  case  of  calcination  previous  to  smelting  in  reverbera- 
tories,  it  is  well  to  avoid  an  excess  of  air  toward  the  close  of 
the  roasting  process ;  a  precaution  easily  effected  by  closing 
the  working  openings  as  far  as  possible,  the  rabble  passing 
through  a  hole  in  the  center  of  a  divided  door,  while  the  pas- 


THE   CHEMISTRY   OF  THE   CALCINING  PROCESS.  163 

sage  of  any  considerable  proportion  of  undecomposed  air 
through  the  grate  is  rendered  unlikely  by  the  lively  fire  that 
belongs  to  this  period.  By  these  precautions,  the  oxidation 
of  any  large  proportion  of  the  iron  present  to  a  sesquioxide  is 
prevented,  the  latter  being  infusible  and  unfit  to  enter  the  slag 
until  it  is  reduced  to  a  protoxide.  This  reduction  takes  place 
instantaneously  in  the  powerful  carbonic  oxide  atmosphere  that 
prevails  in  the  blast-furnace ;  but  in  the  almost  neutral  atmo- 
sphere of  the  ordinary  reverberatory,  the  sulphur  alone  plays 
the  part  of  a  reducing  agent,  and  a  charge  composed  of  the 
sesquioxide  of  iron  will  be  found  materially  to  delay  the 
process  of  fusion,  besides  producing  a  thick  and  foul  scoria. 
The  natural  remedy  is  the  admixture  of  a  few  per  cent,  of  fine 
coal  stirred  thoroughly  into  the  mass  of  the  ore,  and  fired  on 
vigorously. 

An  examination  of  the  preceding  analyses  shows  what  a 
large  proportion  of  the  sulphur  in  the  charge  will  go  into  the 
matte,  especially  in  the  case  of  rapid  smelting  in  blast-fur- 
naces. 

Some  kind  of  an  idea  may  be  obtained  of  the  probable 
composition  of  the  matte  to  be  produced  at  any  given  time 
by  the  ordinary  "  matte  fusion  assay,"  as  given  in  all  works 
on  assaying,  wherein  the  ore  to  be  tested  is  rapidly  melted 
with  merely  enough  borax  and  siliceous  flux — say  100  per 
cent,  of  borax  and  an  equal  amount  of  pulverized  window- 
glass — to  flux  its  earthy  constituents,  some  10  per  cent,  of  argols 
or  other  reducing  agent  being  also  added. 

But  the  results  are  far  from  satisfactory,  and  after  patiently 
using  it  for  some  two  years,  and  being  oftener  misled  than 
guided  by  its  results,  I  discarded  it  completely,  and  trusted 
principally  to  the  eye,  occasionally  aided  by  the  following  cal- 
culation, which  gives  better  results  than  any  other  familiar  to 
me : 

Taking  the  contents  of  copper  in  the  charge  as  a  standard 
for  comparison,  sufficient  sulphur  should  be  allotted  to  it  to 
form  a  subsulphide,  the  excess  of  sulphur  still  remaining  being 
supplied  with  sufficient  iron  to  form  a  monosulphide  of  that 
metal.  If  other  metals  are  present,  such  as  lead,  zinc,  or  man- 
ganese, |  of  the  former,  \  the  second,  or  \  the  latter  substance 


164      MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

may  be  first  considered  as  forming  a  monosulphide  with  the 
sulphur,  there  being  in  such  a  case  just  so  much  less  of  the 
metalloid  left  to  take  up  iron.  This  rule  gives  quite  accurate 
results  in  rapid  blast-furnace  smelting,  and  where  abundance 
of  iron  is  present.  If  the  rate  of  smelting  be  slow,  and  con- 
siderable lime,  magnesia,  or  baryta  is  present,  5  per  cent,  of 
the  sulphur  contents  of  the  charge  should  be  deducted  before 
beginning  the  calculation ;  and  if  the  smelting-furnace  is  a 
reverberatory,  the  resulting  matte  will  average  8  per  cent, 
higher  in  copper  than  found  by  this  formula. 

A  simple  illustration  will  make  this  method  of  calculation 
more  clear. 

We  will  assume  that  a  roasted  ore  having  the  following 
composition  is  to  be  smelted  in  a  blast-furnace  : 

ANALYSIS    OF    CALCINED    OEE. 

Cu    =»      9'0  per  cent.  Pb  =  2'0  per  cent. 

Fe    =    45'0  per  cent.  S*    =  7'8  per  cent. 

Si02  =    27-0  per  cent.  0  and  loss  =  7'2  per  cent. 

Zn     =     2'0  per  cent. 

Total,  100  00  per  cent. 

Calculation  of  matte  which  should  result  from  fusion  of  the 
calcined  ore. 

Following  the  rule  given, 

9  Cu  require  1'8  S  to  form  a  subsulphide. 
|  of  2  Pb        "      0-2  S  to  form  a  sulphide, 
i  of  2  Zn        "      0-3  S  to  form  a  sulphide. 

This  provides  for  2 '3  per  cent,  of  the  7*8  per  cent,  of  sul- 
phur present,  leaving  5'5  per  cent,  which  will  take  up  enough 
Fe  to  form  a  monosulphide.  Calculation  shows  that  9'6  per 
cent,  of  Fe  will  thus  be  required,  leaving  35*4  per  cent,  avail- 
able for  the  slag. 

In  order  to  express  the  composition  of  the  matte  just  calcu- 
lated, in  the  ordinary  manner,  we  multiply  the  amount  of  each 

*  As  most  of  the  oxidized  compounds  of  sulphur  contained  in  the  calcined 
ore  will  be  reduced  to  sulphides  in  the  cupola  furnace,  it  is  proper  to  esti- 
mate all  the  sulphur  present  as  metallic  sulphur. 


THE   CHEMISTKY  OF  THE   CALCINING  PEOCESS.  165 

ingredient  by  a  common  factor  that  will  reduce  it  to  a  percent- 
age.    In  this  case  the  factor  is  346. 

9  Cu  +  1-8  S  —  10-8  x  3-46  =  37'36  percent.  Cu2S. 
l-5Pb  +  0-2S  =    1-7  x  3-46=    5'88  "      "      PbS. 

lZn+0-3S  —    1-3x3-46=    4'5     "      "       ZnS. 
9-6  Fe  +  5-5  S  —  15'1  x  3'46  —  52-26  "      "       FeS. 


7'8  per  cent.  S.  100 -00  per  cent. 

Tims  the  matte  from  such  a  charge  will  contain  about  30 
per  cent,  copper ;  the  slight  loss  of  sulphur  by  volatilization 
and  as  SO2  being  usually  fully  balanced  by  the  presence  in 
the  matte  of  a  certain  proportion  of  subsulphides  in  place  of 
sulphides,  or  even  of  metallic  iron. 

The  same  charge  smelted  in  a  reverberatory  furnace  would 
yield  a  matte  of  nearly  40  per  cent  Cu. 

The  proper  composition  of  the  slag  has  not  been  particu- 
larly considered  in  this  example.  It  would  be  somewhat  too 
siliceous  for  blast-furnace  work,  requiring  the  addition  of  a 
little  limestone ;  while  for  reverberatory  work,  it  would  be 
about  right  as  it  stands. 

From  the  foregoing  statements,  it  is  evident  that  in  ordinary 
copper  smelting  the  calcination  of  sulphide  ores  need  seldom 
be  pushed  to  the  point  of  perfection  indicated  when  treat- 
ing of  the  chemical  reactions  that  take  place  in  the  roasting. 
On  the  contrary,  a  due  regard  for  the  proper  quality  of  the  re- 
sulting matte  and  slag  will  probably  render  it  advisable  to  stop 
the  calcining  process  long  before  the  decomposition  of  the  sul- 
phate of  copper  in  the  charges  is  complete,  and  even  while  a 
considerable  portion  of  undecomposed  sulphides  still  remains. 
If,  however,  the  calcination  has  been  carried  too  far,  it  is  very 
easy  to  regulate  matters  by  the  addition  to  the  smelting  mix- 
ture of  a  very  small  proportion  of  raw  sulphuret  ore. 

A  glance  at  the  behavior  of  the  various  compounds  of  sul- 
phur and  bases  is  essential  for  the  clear  understanding  of  the 
much  greater  richness  of  the  matte  resulting  from  the  fusion 
of  any  given  charge  in  a  reverberatory  than  in  a  blast-furnace, 
and  of  the  importance  of  having  a  certain  proportion  of  sul- 
phates and  other  oxidized  compounds  in  the  smelting  mix- 
ture, in  order  that  they  may  react  on  each  other  in  the  manner 


166     MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

best  calculated  to  eliminate  the  residual  sulphur,  and  thus  in 
a  measure  make  up  for  imperfect  roasting. 

In  the  blast-furnace,  but  little  sulphur  can  be  directly  vol- 
atilized, and,  consequently,  simply  fuses  with  the  copper  or 
iron  present  to  form  the  artificial  sulphide  called  matte.  But 
the  sulphates  in  the  presence  of  carbonic  oxide  may  undergo 
the  following  reaction  :  CO  +  FeO,SO3  =  CO2  +  SO2  +  FeO  ; 
the  carbonic  oxide  burning  to  acid,  while  the  sulphuric  acid  is 
reduced  to  sulphurous  acid,  which  escapes  by  volatilization, 
and  the  protoxide  of  iron  unites  with  silica  to  form  a  slag. 
But  this  is  true  of  only*  a  very  small  proportion  of  the  sul- 
phates present,  as  in  the  powerful  reducing  atmosphere  of  the 
blast-furnace,  the  sulphurous  acid,  even  when  once  formed, 
comes  in  contact  with  an  overwhelming  proportion  of  CO, 
which  in  burning  to  CO2  robs  the  SO2  of  its  oxygen,  reducing 
it  to  sulphur,  in  which  condition  it  unites  with  iron  or  copper 
and  enters  the  matte,  thus  increasing  the  amount  of  this  pro- 
duct, while  it  robs  the  slag  of  its  most  valuable  constituent.  It 
is  interesting  to  note  the  striking  difference  of  the  reaction  in 
the  reverberatory  furnace,  where  the  atmosphere  may  be  re- 
garded as  neutral ;  CO,  the  most  powerful  reducing  agent, 
being  virtually  wanting : 

Cu2S  +  4  CuO,S03  —  6  CuO  +5  SO2. 
Cu2S  +  2CuO,S03  =  2Cu2O  +3  S02. 
Cu2S+2Cu20  =6Cu  +S02. 

By  studying  these  formulae — taken  from  Percy,  Kerl,  and 
Rivot — it  will  no  longer  seem  strange  that  the  reverberatory 
produces  so  much  richer  matte  than  the  blast-furnace  from  the 
same  charge.  Nearly  all  the  reactions  between  sulphides  and 
sulphates  result  in  the  formation  of  oxides  and  volatile  SO2,  and 
were  it  not  for  an  almost  invariable  preponderance  of  undecom- 
posed  sulphides  in  the  charge,  the  elimination  of  the  sulphur 
might  theoretically  be  almost  complete.  It  is  by  this  all- im- 
portant but  frequently  neglected  establishment  of  a  proper 
proportion  between  the  sulphides  and  sulphates,  that  extraor- 
dinary results  may  be  obtained  in  reverberatory  smelting,  and 
the  roasting  plant  greatly  reduced. 

Although  treating  of  smelting,  this  matter  belongs  strictly 
to  the  calcining  department,  and  presents  a  field  for  study  of 


THE   CHEMISTRY  OF  THE   CALCINING  PROCESS.  167 

great  interest  and  practical  value.  A  close  analogy  may  be 
found  in  the  various  reverberatory  processes  as  applied  to  the 
smelting  of  galena  ores,  where  almost  exactly  the  same  results 
are  produced,  using  lead  instead  of  copper,  and  obtaining  me- 
tallic lead  with  a  minimum  amount  of  calcination,  and  by  put- 
ting to  accurate  practical  use  the  reactions  just  explained, 
although  text-books  on  copper  metallurgy  are  strangely  silent 
on  this  important  subject. 

The  length  of  time  requisite  to  roast  a  charge  of  ore  of  a 
given  weight  in  the  long  furnace  under  discussion  depends,  of 
course,  upon  the  composition  of  the  charge  and  the  degree  of 
thoroughness  in  oxidation  desired.  Each  of  the  four  hearths 
of  this  furnace  has  an  effective  area  of  about  250  square  feet, 
and  can  consequently  receive  4,000  pounds  of  ore  if  only  16 
pounds  to  the  square  foot  are  charged.  This  is  a  very  moderate 
charge,  especially  for  heavy  sulphide  ores,  but  will  ordinarily 
give  better  results  than  a  heavier  burden.  It  will  cover  the 
hearth  about  2J  inches  deep  when  charged,  increasing  in  bulk 
to  about  4  inches  at  the  completion  of  the  process.  By  shift- 
ing each  charge  every  four  hours,  the  ore  will  remain  16  hours 
in  the  furnace,  a  time  generally  ample  to  produce  the  desired 
effect.  On  this  basis,  the  furnace  would  put  through  12  tons 
in  twenty-four  hours,  which  may  possibly  be  increased  to  16 
tons  by  substituting  three-hour  drops  for  the  four  hours  rec- 
ommended. But  this  is  the  extreme  limit  for  two  men  per 
shift,  nor  will  these  figures  be  reached  under  ordinary  circum- 
stances. Two  cords  of  wood  or  2,240  pounds  of  soft  coal 
should  supply  the  grate  for  twenty-four  hours,  the  supply  of 
air  to  the  ash-pit  being  kept  at  the  lowest  possible  point.  The 
sulphur  contents  of  the  ore  furnish  a  much  greater  proportion 
of  the  heat  than  does  the  fuel  on  the  grate. 

The  manipulations  pertaining  to  the  ordinary  calcination 
of  ore  are  too  simple  and  generally  known  to  be  worthy  of  a 
place  in  a  condensed  treatise. 

The  following  experiments  form  part  of  a  series  extending 
over  some  ten  years,  which  it  was  at  one  time  hoped  to  am- 
plify and  carry  out  into  something  of  positive  value.  But  in- 
creasing professional  cares,  and  the  impossibility  of  having  the 
numerous  analyses  made  that  constitute  an  essential  part  of 


168     MODERN"  AMERICAN  METHODS   OF   COPPER  SMELTING. 


the  work,  have  prevented  the  fulfillment  of  this  hope.  The 
material  collected  will,  however,  be  used  wherever  it  may  prove 
of  value  in  the  course  of  this  treatise.  The  author  desires  to 
acknowledge  the  assistance  of  Messrs.  J.  F.  Talbot  and  F. 
Ames,  and  others,  in  the  chemical  portion  of  the  work. 


•si 
II 

I 

Sulphur. 

£j2 

ft! 

IN 

T  o 
£~ 

Copper  in  roasted  ore. 

Sulphur  in 
roasted  ore. 

5,5 

*I 

5  £ 
ffl£ 

16 
12 

18 

24 
18 

18 
18 

EEMARKS. 

fcjj 

mfi 

•< 

is 

^ 

r-i  ai 

si 

«3ft 

1 

1... 
2... 

3... 

4... 
5... 

6... 

7.  .  . 

Pr  ct. 
7'6 
7-6 

16-4 

16'4 

38-8 

62'2 

74-8 

Pr  ct. 
37'0 
39-0 

31-0 

31'0 
24  3 

22'0 
21-4 

Lbf. 
4,130 
4,130 

b,925 

3,940 
3,600 

3,580 
3,800 

Pr  ct. 
14-5 
11-8 

6'4 

9-5 
62 

3-7 

2'4 

3-65 
2'27 

7'10 

12-80 
29-20 

54-90 
61-60 

3-25 
3'10 

3-44 

2-80 
4-40 

3-80 
5  40 

1-65 

2'80 

6'80 

2'10 
3-70 

6-60 
7-90 

8'55 
8-17 

17-34 

17-70 
37-30 

64-30 
74-90 

6-41 
11-30 

8'20 
4'60 

Heavy  pyritous  ore. 
Same  ore. 
(  Purple     ore     with 
•<     much  pyrites  and 
f     some  zmcblende. 
Same  ore. 
Matte  from  cupola. 
(Blue     metal    from 
{     reverberatory. 
(White  metal    from 
j     reverberatory. 

The  loss  of  weight  from  the  removal  of  the  sulphur  is  par- 
tially balanced  by  the  oxygen  combining  with  the  metallic 
bases,  and  is  exceedingly  variable,  as  may  be  seen  by  this 
table. 

The  loss  in  copper  during  calcination  is  very  small,  and 
almost  entirely  mechanical,  being  for  the  most  part  recover- 
able where  proper  arrangements  are  made  for  the  deposition 
of  the  flue-dust.  Average  results  from  personal  experience 
show  a  loss  of  about  1 J  per  cent,  of  the  original  copper  con- 
tents of  the  ore  during  calcination. 

This  flue-dust  is  usually  of  very  much  lower  grade  than  the 
ore  from  which  it  results,  being  diluted  with  the  dust  from  the 
fluxes,  fuel,  etc.,  and  generally  contains  from  20  to  30  per  cent, 
of  its  value  in  a  soluble  form,  thus  prohibiting  the  use  of  water 
as  an  aid  to  its  condensation,  unless  provision  is  made  to  pre- 
cipitate the  dissolved  metal. 

Unless  the  ores  treated  are  of  remarkable  purity,  it  is  best 
to  smelt  the  flue-dust  by  itself,  making  it  into  balls  with  clay 
or  lime  and  adding  the  necessary  fluxes.  Otherwise,  the  qual- 
ity of  the  metal  is  likely  to  suffer,  as  the  substances  most  inju- 
rious to  it — arsenic,  antimony,  and  tellurium — are  volatile, 
and  sure  to  be  condensed  in  the  flues,  thus  being  collected  in 
a  concentrated  form. 


THE  CHEMISTRY   OF  THE   CALCINING  PROCESS.  169 


COST    OF   CALCINING. 

The  running  expenses  of  a  calciner,  aside  from  the  slight 
repairs  just  alluded  to,  are  small  and  regular.  In  twenty-four 
hours,  it  will  burn  one  ton  of  soft  coal  (2,240  pounds)  at  $5,  or 
2  cords  of  pine  wood,  and  require  the  services  of  four  men  at 
$2,  and  one  quarter  the  time  of  a  laborer  to  weigh  and  bring 
the  charges  to  the  hoppers,  the  furnace-men  dumping  and 
drawing  their  own  charges.  This  amounts  to — 

Coal ,  1  ton $5.00 

4  furnace-men  at  $2 8.00 

i  weigher  at  $2 . 50 

Wear  and  repairs  on  tools,  car,  etc 30 

Oil,  lights,  and  miscellaneous 80 

Proportion  of  superintendence  (say  one  foreman  to  eight  furnaces).     .50 


Considering  that  twelve  tons  per  day  of  highly  sulphureted 
ores  can  be  quite  thoroughly  calcined  in  such  an  apparatus,  it 
shows  a  cost  of  about  $1.25  per  ton  of  ore,  which  leaves  but 
little  opportunity  for  the  inventors  of  automatic  roasting- fur- 
naces to  cheapen  the  results  that  can  be  obtained  in  the  old- 
fashioned  calciner,  when  built  of  proper  dimensions  and  pro- 
vided with  a  powerful  draught.  The  above  figures  have  been 
repeatedly  obtained  by  the  author  (reduced,  of  course,  to  cur- 
rent prices),  and  after  a  tolerably  extended  metallurgical 
experience  and  a  trial  of  almost  every  reasonable  type  of 
roasting  apparatus,  he  still  emphatically  recommends  the  sim- 
ple and  well-known  open-hearth  reverberatory  calciner  for  the 
preliminary  roasting  of  copper  ores  and  mattes. 

The  consumption  of  fuel  depends  largely  upon  the  fireman. 
It  is  as  easy  for  him  to  burn  two  tons  of  coal  as  one ;  but  in  a 
properly  constructed  furnace,  with  a  moderately  favorable  ore 
carrying  20  per  cent,  or  more  of  sulphur,  the  quantity  above 
indicated  will  suffice  perfectly. 


CHAPTER  IX. 

THE   SMELTING  OF  COPPER. 

BY  this  term,  we  understand  the  fusion  of  the  copper-bear- 
ing material  and  of  whatever  fluxes  may  be  necessary,  when 
the  copper,  owing  to  its  higher  specific  gravity,  separates  from 
the  slag,  and  is  recovered  by  appropriate  means.  In  the  case 
of  oxidized  ores,  it  is  obtained  at  once  in  a  metallic  condition, 
somewhat  adulterated  with  sulphur,  iron,  and  other  foreign 
substances,  but  requiring  only  a  single  operation,  or,  at  the 
outside,  two  more  operations,  to  bring  it  into  merchantable 
form. 

But  when  it  occurs  in  combination  with  sulphur  or  arsenic, 
and  accompanied  with  an  excess  of  foreign  sulphides,  the  re- 
sult of  the  first  fusion  is  merely  a  concentrated  ore,  freed  from 
the  earthy  gangue,  and  resulting  from  a  combination  of  the 
copper  with  sufficient  of  the  sulphur  present  to  form  a  sub- 
sulphide,  to  which  is  added  as  much  monosulphide  of  iron  as 
corresponds  to  the  remaining  sulphur,  always  excepting  such 
portion  of  that  metalloid  as  is  volatilized  during  the  process  of 
fusion.  If  tin,  zinc,  lead,  silver,  antimony,  or  arsenic  are  pres- 
ent, they  combine  with  the  sulphur  for  the  most  part  and  enter 
the  matte,  their  affinity  to  sulphur  being  in  the  order  men- 
tioned, according  to  Fournet's  experiments. 

These  various  sulphides  unite  either  physically  or  chem- 
ically to  form  the  substance  technically  known  as  matte,  or 
metal,  or  regulus,  the  latter  term  not  to  be  confounded  with 
the  term  regule,  which  belongs  to  a  matte  of  a  certain  rich- 
ness in  copper,  and  possessing  peculiar  and  well-marked  char- 
acteristics. 

From  the  above  statements,  it  is  plain  that,  other  things 
being  equal,  the  grade  of  the  matte  depends  on  the  amount  of 
sulphur  in  the  ore. 

It  might,  at  first  glance,  seem  more  economical  to  push 


THE   SMELTING   OF   COPPER.  171 

the  roasting  process  to  the  extent  of  removing  all  the  sulphur, 
thus  bringing  about  the  same  conditions  that  prevail  in  the 
smelting  of  an  oxidized  ore ;  but  practice  has  shown  the  futil- 
ity of  such  a  scheme,  as,  aside  from  the  great  expense  and 
difficulty  of  effecting  such  a  complete  calcination,  the  resulting 
slags  are  always  too  rich  in  copper ;  the  smelting  process  suf- 
fers for  want  of  oxidized  iron  to  neutralize  the  silica,  and  the 
copper  when  produced  cannot  compare  in  quality  with  the 
metal  resulting  from  the  ordinary  methods  of  treatment,  where 
the  numerous  alternate  oxidizing  and  reducing  influences 
remove,  for  the  greater  part,  those  traces  of  impurities  that 
are  almost  invariably  present,  even  in  the  purest  ores,  and 
which  have  such  a  powerful  effect  on  the  physical  condition  of 
the  finished  metal. 

Copper  smelting,  therefore,  is  naturally  separated  into  two 
great  divisions,  according  to  the  composition  of  the  material  to 
be  treated  :  1.  Smelting  of  ores  containing  sulphur  (arsenic, 
antimony).  2.  Smelting  of  ores  free  from  sulphur  (etc.).  But 
each  of  these  classes  may  be  again  divided,  according  to  the 
apparatus  employed,  into — 

A.  Smelting  in  blast-furnaces. 

B.  Smelting  in  reverberatory  furnaces. 

But  few  exact  statements  have  been  published  by  practical 
metallurgists  of  comparative  results  obtained  by  running  the 
two  classes  of  furnaces  side  by  side  on  the  same  ore,  and  under 
the  same  management  and  conditions.  The  fact  that,  during 
the  author's  career  as  manager  of  various  copper  works,  he  has 
smelted  about  an  equal  amount  of  ore  in  each  class  of  furnace, 
and  in  several  instances  carried  out  quite  extensive  compara- 
tive tests  at  the  same  works  as  to  cost,  capacity,  etc.,  may  lend 
value  to  such  statements. 

Considerable  animosity  has  been  evinced  by  the  partisans  of 
the  reverberatory  and  of  the  blast-furnace  system  of  treatment 
— or  Swansea  and  German  methods,  as  they  are  often  termed. 
Much  of  this  arises  from  a  want  of  exact  knowledge  and  appre- 
ciation of  the  advantages  and  peculiarities  of  the  opposing 
systems. 

Since  blast-furnace  smelting  has  obtained  a  footing  in  the 
United  States,  it  has  become  so  changed  from  its  original  as 


172     MODERN   AMERICAN   METHODS   OF   COPPER  SMELTING. 

to  be  scarcely  recognizable,  and  as  here  used,  by  the  more 
advanced  metallurgists,  can  challenge  competition  with  the 
reverberatory  under  most  circumstances,  and,  where  the  condi- 
tions are  at  all  favorable,  can  show  results  far  surpassing  the 
best  Swansea  work  in  yield,  economy,  and  capacity. 

That  this  may  seem  novel  or  even  doubtful  to  English 
smelters,  is  quite  natural,  when  it  is  recollected  that  the  full 
extent  of  these  remarkable  advances  is  known  to  comparatively 
few  metallurgists,  and  that  very  little  relating  to  the  same  has 
been  published. 

It  is  with  the  modern  American  form  of  the  German  copper 
process  that  all  comparisons  must  be  instituted  ;  and  this  com- 
prises not  only  a  great  improvement  in  the  processes  of  calcina- 
tion and  the  construction  and  management  of  the  blast-furnaces 
used,  but,  in  many  cases,  the  employment  of  reverberatories  for 
certain  portions  of  the  matte  concentration,  while  the  process 
of  refining  is  in  all  cases  carried  on  according  to  the  Swansea 
method. 

In  any  attempt  at  a  comparison  of  these  two  great  methods 
of  smelting,  one  is  confronted  by  the  inextricable  mingling  of 
the  commercial  with  the  metallurgical  that  is  so  characteristic 
of  the  English  system.  Without  a  thorough  understanding  of 
the  peculiar  local  conditions  under  which  the  ores  are  purchased 
at  the  Swansea  ticketings,  it  is  impossible  fully  to  appreciate  the 
fine  points  of  the  complex  and  ingenious  system  that  time  and 
circumstances  have  elaborated,  or  to  realize  the  important  in- 
fluence exercised  on  the  whole  subsequent  series  of  operations 
by  the  amount  of  judgment  displayed  in  the  purchase  of  the 
ores,  and  in  the  adaptation  of  the  same  to  the  immediate  needs 
of  the  works.*  The  Swansea  smelter  receives  his  ore  in  num- 
berless small  parcels,  differing  not  only  in  richness,  but  in 
purity  and  other  qualities.  To  carry  out  the  reverberatory 
process  to  the  best  advantage,  he  requires,  in  addition  to  the 
main  supply  of  sulphide  ores,  a  certain  proportion  of  oxides  and 
carbonates,  all  of  which  are  obtainable  in  the  public  ore  market. 
Ilis  coal  is  of  the  cheapest  and  most  suitable  quality,  and  the 


*  See  Percy  on  Copper  for  a  full  description  of  the  Swansea  ore  sales, 
together  with  quality  and  value  of  ore  offered. 


THE   SMELTING  OF  COPPEE.  173 

refractory  material — fire-brick,  clay,  siliceous  sand,  etc. — is  ob- 
tainable at  prices  far  below  American  rates.  He  also  has  at  his 
command  a  body  of  experienced  and  skillful  workmen  who 
have  grown  up  at  the  furnaces,  and  who,  at  very  low  wages, 
are  fully  capable  of  executing  all  the  difficult  operations  de- 
manded by  this  system  of  treatment.  In  addition,  he  has  a 
market  for  his  product,  where  every  variety  of  metal  brings  the 
highest  justifiable  price. 

Jt  is  very  evident  that  such  a  state  of  affairs  cannot  be  com- 
pared with  average  American  conditions,  where,  in  the  greater 
number  of  instances,  the  ore  supply  comes  from  only  one  or 
two  sources,  constant  in  its  composition,  and  usually  in  very 
large  quantities.  This,  with  the  high  wages  and  exceedingly 
expensive  fuel,  has  caused  the  introduction  of  labor-saving  ma- 
chinery and  appliances  to  an  unprecedented  extent,  as  well 
as  a  constant  endeavor  to  lessen  the  proportion  of  fuel  to  ore 
smelted.  The  lack  of  steady  and  skilled  furnacemen,  and  the 
high  cost  of  refractory  materials,  have  also  had  a  powerful  influ- 
ence in  shaping  the  processes  of  treatment,  and  have  perfected 
the  water-jacketed  cupola,  without  which  many  of  our  most  suc- 
cessful metallurgical  enterprises  could  hardly  exist.  The  same 
influences  have  concentrated  the  works  for  the  refining  of  copper 
in  a  very  few  hands,  and  located  them  with  the  view  to  cheap  coal 
and  refractory  materials  and  to  a  market  for  the  finished  pro- 
duct. Another  factor  that  has  had  its  effect  in  greatly  simpli- 
fying our  domestic  process  of  refining  is  the  extreme  purity  of 
the  lake  copper,  which,  in  this  country,  takes  the  place  of  the 
higher  grades  of  English  copper,  there  produced  by  special 
refining  processes,  and  commands  correspondingly  higher 
prices. 

BLAST-FURNACE  SMELTING. 

a.  Of  sulphide  ores. 

b.  Of  ores  free  from  sulphur. 

a. — TBEATMENT  OF  SULPHIDE   OEES. 

The  fusion  of  sulphide  ores  in  blast-furnaces  may  take 
place  either  with  or  without  a  previous  calcination,  as  has  been 
already  referred  to. 

Where  the  percentage  of  sulphur  is  small  in  proportion  to 


174     MODERN  AMERICAN  METHODS   OF   COPPER   SMELTING. 

the  copper  contents,  a  sufficiently  high-grade  matte  may  be 
obtained  by  the  direct  fusion  of  the  raw  ore,  with  the  addition, 
of  course,  of  the  proper  quantity  of  basic  substances,  such  as 
iron  ore,  limestone,  etc.,  to  flux  the  very  large  proportion  of 
gangue  rock,  which,  in  most  cases,  consists  of  quartz  or  some 
highly  siliceous  substance.  As  the  amount  of  basic  material 
required  to  flux  silica  is  very  large,  about  two  pounds 
to  one  of  silica,  highly  siliceous  ores  can  be  remuneratively 
smelted  only  under  exceptionally  favorable  circumstances. 
Otherwise,  such  ores  would  often  be  more  advantageously 
treated  by  one  of  the  wet  processes.  No  better  flux  for 
silica  can  be  had  than  the  ferruginous  slag  arising  from  the 
concentration-smelting  of  copper  mattes,  which  usually  con- 
tains about  one  per  cent,  of  copper,  but  can  seldom  be  obtained 
in  such  quantities  as  to  form  a  permanent  flux  for  any  consid- 
erable amount  of  highly  siliceous  ore. 

The  class  of  copper  ore  most  commonly  subjected  to  blast- 
furnace treatment  in  the  Eastern  portion  of  this  country  is  a 
highly  pyritous  material,  usually  having  from  2  to  6  per  cent, 
of  copper,  and  varying  amounts  of  silica.  This  is  first  burned 
for  the  manufacture  of  sulphuric  acid,  after  which  the  cinders 
are  smelted  for  copper.  The  ores  from  Capelton,  Province 
of  Quebec ;  Milan,  New  Hampshire  ;  Virginia  ;  and  Georgia 
carry  an  excess  of  iron,  and  to  them  may  be  added  the  mono- 
sulphide  ores  found  at  Ely  and  Copperas  Hill,  Vermont ; 
Ducktown,  Tenn. ;  and  Ore  Knob,  North  Carolina.  In  the 
West,  a  large  number  of  mines  furnish  copper  ores  usually  of 
somewhat  greater  richness,  but  in  which  the  silica  is  in  excess, 
rendering  the  smelting  more  difficult  and  occasionally  making 
the  employment  of  reverberatory  furnaces  advisable.  To  this 
class  belong,  also,  the  ores  of  the  Douglas  and  many  other 
Maine  deposits;  the  St.  Grenevieve,  Mo.,  mines  ;  a  large  class 
of  argentiferous  copper  mines  in  San  Juan  District,  Colorado ; 
most  of  the  Butte  City  veins ;  and  a  series  of  important  though 
little  known  deposits  in  Lower  California  and  Nevada.  This 
brief  enumeration  includes  most  of  the  types  of  sulphide  ore 
likely  to  come  to  the  blast-furnace  ;  and  the  first  object  of  the 
metallurgist  is  to  see  how  he  can  form  a  proper  slag  at  the  least 
possible  cost. 


THE  SMELTING  OF   COFFEE.  175 

A  proper  slag  for  a  blast-furnace  should  contain  between  24 
and  36  per  cent,  of  silica,  although,  under  pressure  of  circum- 
stances, these  extreme  figures  may  be  either  raised  or  lowered 
about  6  per  cent,  without  seriously  compromising  the  running 
of  the  furnace.  But  every  per  cent,  of  silica  in  excess  of  36 
will  be  felt  in  a  rapid  reduction  of  the  amount  smelted  in 
twenty-four  hours. 

As  it  is  usually  a  long  time  before  the  young  metallurgist 
fully  appreciates  the  enormous  damage  that  even  a  slight  ex- 
cess of  silica  will  effect,  the  writer  desires  particularly  to  em- 
phasize this  point,  and  to  declare  that,  according  to  his  own 
experience,  three-fourths  of  the  troubles  and  annoyances  exper- 
ienced by  the  blast-furnace  manager  result  from  this  cause. 
There  are  many  instances  of  furnaces  that  have  given  trouble 
from  the  day  of  their  first  starting  being  relieved  by  a  slight 
addition  of  iron  ore,  and  smelting  operations  have  changed 
from  a  loss  to  a  profit,  capacity  been  increased  40  per  cent., 
and  the  campaign  lengthened  from  20  days  to  several  months 
by  slightly  increasing  the  insufficient  charge  of  limestone  and 
iron. 

In  speaking  of  modern  blast-furnace  smelting,  we  may  well 
omit  any  lengthy  description  of  the  small  brick  furnaces  so 
familiar  to  all  who  look  over  the  illustrations  in  Kerl  and  Platt- 
ner.  The  economy  of  larger  furnaces  has  been  thoroughly 
demonstrated,  and  in  the  present  treatise,  plans  and  descrip- 
tions will  be  mostly  confined  to  the  two  principal  types  of  fur- 
nace now  in  use : 

1.  The  water-jacket  furnace,  with  its  various  modifications. 

2.  The  long  rectangular  brick  furnace. 

With  a  thorough  understanding  of  the  construction  and 
management  of  these  two  varieties  of  furnace,  the  metallurgist 
is  amply  prepared  to  obtain  the  best  results  known  to  modern 
engineers. 

1.  The  water-jacket  furnace,  with  its  various  modifications. 

Without  attempting  to  determine  to  whom  the  credit  be- 
longs of  adapting  the  principle  of  water-cooling  to  copper 
blast-furnaces,  it  may  be  hailed  as  the  greatest  advance  in  the 
treatment  of  that  metal  that  has  been  made  since  the  intro- 
duction of  the  English  method  of  refining  on  the  hearth  of  a 


176     MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

reverberatory  furnace.  With  its  employment,  the  burning 
out,  and  consequent  "  freezing  up,"  of  the  furnace  from  the 
half-fused  masses  of  molten  fire-brick,  have  become  things  of 
the  past,  and  campaigns  have  been  extended  to  an  unprece- 
dented length.  In  fact,  where  no  accident  occurs,  nothing 
compels  the  stoppage  of  the  furnace  excepting  the  need  of 
general  repairs  to  machinery,  etc.;  the  cleansing  of  the  interior 
of  the  jacket  from  sediment ;  and  the  possible  choking  up  of 
the  furnace  shaft  with  accretions  of  sulphides  of  zinc  or  lead, 
which  occur  in  minute  proportions  in  almost  all  copper  ores. 

The  material  of  which  the  jacket  is  composed  may  con- 
sist of  cast-iron,  wrought-iron,  or  mild  steel.  The  brand  of 
wrought-iron  known  as  fire-box  iron  is  preferred  by  the  author, 
as  less  liable  to  scale  and  blister  by  the  heat,  and  because 
capable  of  being  bent  without  weakening.  Where  cast-iron 
is  used,  the  furnace  is  composed  of  several  sections,  held  to- 
gether by  clamps  or  rings ;  but  aside  from  the  excessive 
weight,  this  material  is  somewhat  liable  to  crack  when  exposed 
to  extreme  fluctuations  of  temperature,  although,  as  of  late  the 
castings  are  made  from  five-eighths  to  three-quarters  of  an  inch 
thick,  with  a  water- space  of  from  four  to  ten  inches,  this  acci- 
dent is  much  less  likely  to  occur.  The  thickness  of  the  wrought 
jackets  need  not  exceed  that  of  ordinary  boiler  plate,  and  this 
material  is  peculiarly  suited  to  circular  furnaces,  the  inner 
plate  having  been  found  to  buckle  and  weaken,  owing  to  dif- 
ference of  expansion,  when  used  in  long  rectangular  furnaces — 
an  observation  made  by  Mr.  J.  B.  S.  Herreshoff,  of  New  York, 
and  which  he  has  obviated  by  using  a  very  elongated  oval 
shape  in  place  of  the  rectangular. 

Although  the  circular  form  possesses  certain  advantages 
for  smelting-furnaces,  experience  has  taught  us  that  the  ordi- 
nary blast  used  in  copper  smelting,  which  seldom  exceeds 
three-quarters  of  a  pound  per  square  inch,  cannot  well  penetrate 
to  the  center  of  a  charge  in  a  furnace  of  greater  diameter  than 
fifty  inches,  this  being  the  outside  limit  in  cases  where  at  least 
one-half  the  charge  is  in  lump  form.  In  wrought-iron  jackets, 
the  width  of  the  water-space  has  been  diminished  little  by 
little,  until  even  two  inches  has  become  a  not  uncommon  stand- 
ard, and  its  reduction  over  several  square  feet  of  surface  to 


THE  SMELTING   OF   COPPEE.  177 

one  and  one-quarter  inches  has  not  been  accompanied  with  any 
evil  results.  The  cold  feed-water  is  generally  introduced  near 
the  middle  or  lower  portion  of  the  jacket,  and  doubtless  settles 
to  the  lower  point  at  once,  rising  gradually  as  it  becomes 
heated,  and  escaping  through  a  pipe  of  somewhat  greater  area 
from  the  upper  portion  of  the  jacket.  It  is  best  to  have  the 
escape-pipe  tapped  into  the  water-space  in  such  a  way  that  it 
is  even  with  the  extreme  upper  surface,  thus  preventing  the 
accumulation  of  any  steam  that  might  form.  Circulating  pipes 
are  introduced  into  the  water-space  by  some  of  the  best  manu- 
facturers; but  while  not  prepared  to  deny  their  value,  the 
author  has  run  water-jacketed  furnaces  of  many  sizes  and 
shapes,  and  under  varying  conditions,  and  has  never  felt  the 
need  of  any  guide-plates,  the  difference  in  temperature  of  the 
incoming  and  outgoing  water  always  being  sufficient  to  keep 
up  a  lively  circulation  to  the  most  distant  point,  while  any 
sediment  introduced  in  the  water  could  always  be  easily 
removed  through  the  hand-holes  provided  for  that  purpose. 

The  following  figures,  deduced  from  personal  experience, 
give  furnaces  of  this  description,  and  of  various  diameters,  and 
the  quantity  of  water  required  when  in  full  blast : 

Water  per  hour  Water  per  hour 

Diam-  while  blowing  during  normal 

eter.  in  and  out.  running. 

Inches.  Galls.  Galls. 

24 900 460 

30 1,200 600 

36 1,450 950 

42 2,200 1,200 

48 3,000 1,500 

These  figures  refer  to  a  supply  of  fresh  water ;  but  where 
the  same  water  is  used  over  and  over  again,  about  3,000  gal- 
lons per  twenty-four  hours  are  required  to  make  up  the  loss  by 
evaporation,  etc.,  in  a  36-inch  furnace  in  the  dry,  hot  climate 
of  Arizona.  Prof.  F.  L.  Bartlett  has  arranged  a  tank  at  such 
a  height  that  its  upper  surface  is  a  trifle  higher  than  the 
water  level  in  the  jacket,  by  which  means  a  constant  circula- 
tion takes  place,  requiring  only  the  addition  of  sufficient  fresh 
water  to  replace  the  evaporation.  This  may  require  a  little 
extraneous  aid  from  a  force-pump  or  steam-jet  during  the 
12 


178     MODERN  AMERICAN  METHODS   OF  COPPEE  SMELTING. 

period  of  blowing  in ;  but  in  a  few  hours,  when  the  upper  por- 
tion of  the  furnace  is  cooled  down  to  its  normal  condition,  this 
arrangement  is  said  to  answer  every  purpose,  though  the 
water  may  from  time  to  time  become  a  little  hot  and  even 
form  a  certain  amount  of  steam.  To  save  all  calculation,  it 
may  be  stated  that  a  2J-inch  feed-pipe,  with  a  2|  discharge- 
pipe,  the  former  coming  from  a  tank  that  will  give  eight  or  ten 
feet  pressure,  will  give  all  the  water  necessary  for  a  42-inch 
furnace. 

Where  the  hot  discharge-water  is  not  used  over  again,  it  is 
economical  to  employ  it  for  the  boiler,  or  in  winter  to  lead  it 
into  some  lower  tank,  or  where  it  may  be  used  for  ore  concen- 
tration purposes,  if  such  a  plant  is  present.  The  furnace 
jacket  should  always  be  provided  with  a  drain-cock,  to  empty 
it  when  not  in  blast  in  cold  weather. 

While  the  weight  and  clumsiness  of  cast  jackets  prevent 
their  being  made  of  any  great  size,  so  that  the  first  jackets 
only  occupied  a  narrow  circular  ring  at  the  level  of  the  tuyeres 
and  for  a  few  inches  above,  it  has  now  become  quite  custom- 
ary to  cast  them  in  sections  of  from  30  to  60  inches  in  height, 
while  the  circular  or  oval  wrought  jackets  usually  extend  from 
a  point  some  10  inches  below  the  tuyeres,  to  the  threshold  of 
the  charging-door,  a  distance  of  from  6  to  10  feet.  This  saves 
all  brick- work,  excepting  the  small  amount  in  the  bottom,  and 
the  flue  on  top,  by  which  the  gases  are  conducted  to  the  stack. 
This  flue  and  upper  brick-work  are  usually  supported  on  light 
iron  columns,  the  jacket  itself  being  either  suspended  from  the 
same  columns  by  a  ring,  or  resting  on  cast  legs  of  its  own. 

The  bottom  of  the  furnace  may  be  constructed  in  various 
ways ;  but  in  the  smelting  of  roasted  pyritic  sulphide  ores, 
American  practice  is  pretty  unanimous  in  entirely  doing  away 
with  the  ordinary  deep  crucible,  substituting  for  it  merely  a 
sloping  bottom  a  foot  or  less  below  the  tuyeres,  from  which  the 
entire  molten  material  escapes  through  a  narrow  groove  under 
the  breast,  then  first  entering  an  outside  crucible  or  "  well,"  in 
which  the  matte  separates  from  the  slag,  and  is  tapped  into 
molds,  while  the  slag  flows  from  a  spout  into  iron  pots  arranged 
on  wheels  for  convenient  dumping.  It  is  this  transfer  of  the 
crucible  from  the  inside  to  the  outside  of  the  furnace  that  has 


THE   SMELTING  OF   COPPER.  179 

divested  cupola  work  of  most  of  its  terrors.  By  this  simple 
means,  we  escape  the  troublesome  chilling  over  of  the  metal  in 
the  crucible,  and  the  frequent  freezing  up  of  the  tap-hole,  ren- 
dering it  impossible  to  empty  the  furnace  without  the  most 
laborious  and  tedious  work.  The  formation  of  sows  and  other 
kindred  products  is  also  prevented  by  the  immediate  escape 
of  the  fused  ore  from  the  powerful  reducing  action  of  the  fuel, 
as  are  also  the  cutting  down  of  the  crucible  and  thinning  of 
its  surrounding  walls  until  the  metal  and  slag  burst  through ; 
and  along  list  of  lesser  troubles,  familiar  to  every  practical  fur- 
nace-man. 

The  advantages  gained  by  modern  blast-furnace  practice 
may  be  partially  estimated  by  comparing  the  following  state- 
ment with  the  results  given  in  succeeding  pages  of  this  trea- 
tise. 

As  a  matter  of  historical  interest,  it  may  be  put  on  record 
that  the  first  "  well "  used  in  connection  with  a  copper  furnace 
in  this  country  was  built  by  James  Douglas,  Jr. ,  at  his  Phoe- 
nixville  works,  in  1879.  The  author  is  unable  to  find  any 
authentic  information  of  any  earlier  use  of  the  modern  form  of 
well,  or  independent  fore-hearth. 

In  a  valuable  and  interesting  lecture  delivered  by  Mr. 
Henry  Hussey  Vivian,  M.P.,  at  Swansea,  December  20th,  1880, 
on  the  history  and  processes  of  copper  smelting,*  after  admit- 
ting that  the  blast-furnace  invariably  excels  all  other  appa- 
ratus in  the  production  of  a  clean  slag  (that  is,  free  from  metal), 
he  adds  that :  "  It  has  a  constant  tendency  to  reduce  the  oxide 
of  iron  contained  in  the  calcined  ore  into  metallic  iron,  and  thus 
to  produce  a  mass  of  infusible  material  at  the  bottom  of  the 
furnace,  which,  in  no  long  period,  causes  the  entire  or  partial 
destruction  of  the  furnace.  Even  in  the  best  managed  conti- 
nental works,  I  have  proofs  that  the  so-called  iron  '  sows '  are 
produced ;  in  fact,  they  are  an  almost  unavoidable  incident  of 

*  Copper  Smelting  :  its  History  and  Processes.  By  Henry  Hussey  Vivian, 
M.P.  A  Lecture  delivered  at  Swansea,  in  the  Theater  of  the  Royal  Institu- 
tion of  South  Wale?,  December  20th,  1880.  {To  which  is  added]  A  History 
of  the  Baltimore  Copper  Works  at  Canton,  Maryland ;  Sketches  of  the  Forest 
Copper  Works,  and  the  Hafod  Copper  Works,  Swansea,  South  Wales. 
With  Illustrations.  New  York:  The  Scientific  Publishing  Com}  any,  27 
Park  Place.  1881.  8vo,  pamphlet. 


180     MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

melting  calcined  copper  ores  in  blast-furnaces."  And  in  refer- 
ring to  his  persona]  examination  of  the  ancient  slag-piles  sur- 
rounding the  famous  Eio  Tinto  and  Tharsis  mines,  in  Spain, 
he  says :  "  I  examined  critically  the  slag-heaps,  and  was  aston- 
ished at  the  freedom  of  the  slags,  made,  perhaps,  two  thousand 
years  ago,  from  prills.  At  this  moment,  with  all  my  accumu- 
lated experience  of  copper  smelting,  I  don't  know  how  they 
made  those  heavy  irony  slags  so  clean." 

If  Mr.  Yivian  had  had  the  use  of  the  blast-furnace  forced 
upon  him  under  these  conditions,  there  is  little  doubt  that  he 
would  have  solved  this  problem  that  now  perplexes  him.  At 
any  rate,  the  Americans  have  solved  it  in  the  most  satisfactory 
manner,  and  can  refer  the  inquirer  to  the  records  and  practice 
of  almost  any  of  the  principal  copper-works  in  this  country, 
where  slags  of  the  most  bighly  ferruginous  character,  as  well  as 
the  most  siliceous,  are  produced  in  blast-furnaces,  not  only  free 
from  prills,  and  without  the  slightest  accompaniment  of  iron 
sows,  but  also  far  lower  in  chemically  combined  copper  than 
can  possibly  be  made  in  reverberatories.  How  such  results 
are  obtained,  will  be  explained  when  treating  of  furnace  man- 
agement, although  the  improved  construction  has  also  an  im- 
portant influence  in  effecting  these  results. 

In  the  treatment  of  sulphide  ores,  the  practice,  formerly 
common,  of  having  the  crucible  wholly  or  in  part  under  the 
main  body  of  the  furnace — as  in  the  German  Tiegel-Ofen  and 
Sump-Ofen — can  under  no  conditions  be  recommended.  Those 
interested  in  this  system  of  furnace  construction  will  find  full 
details  regarding  the  same  in  any  of  the  standard  German 
works  on  the  subject,  and  in  the  section  of  this  treatise  devoted 
to  brick  furnaces. 

The  bottom  of  the  furnace,  according  to  modern  practice,  is 
brought  up  to  within  from  6  to  1'2  inches  of  the  tuyere  level,  in 
most  cases  sloping  slightly  toward  the  breast,  so  that  the  en- 
tire molten  contents  may  flow  out  through  a  narrow  channel 
under  the  latter,  and  discharge  into  an  anterior  compartment, 
consisting  either  of  a  deep  basin  formed  of  "  steep"  (Gestubbe, 
Brasque),  or  a  large  rectangular  box,  made  of  fire-brick  held 
together  by  iron  plates,  and  in  which  the  separation  of  matte 
from  slag  takes  place  quietly  and  thoroughly. 


THE   SMELTING  OF   COPPER.  181 

Provision  is  made  to  prevent  any  escape  of  blast  under  the 
breast,  either  by  so  thoroughly  covering  over  the  orifice  and 
channel  that  only  a  minute  groove  exists,  which  is  constantly 
filled  to  its  utmost  capacity  with  the  molten  ore,  which  soon 
forms  an  impervious  cover  to  its  channel ;  or  by  so  raising  the 
terminal  slag-spout,  and  lowering  the  anterior  wall  of  the  fur- 
nace, that  the  blast  is  securely  "  trapped,"  just  as  sewer  gas  is 
prevented  from  escaping  in  an  ordinary  drain. 

The  first  method,  combined  with  the  steep  crucible,  is  best 
adapted  to  the  production  of  pig- copper  or  very  rich  metal,  as 
in  matte  concentration,  owing  to  the  great  tendency  to  chill  of 
these  substances  ;  while  the  latter  plan  is  far  preferable  for 
ordinary  ore-smelting,  where  matte  of  much  lower  grade  is 
produced  in  considerable  quantities.  "Where  pig-copper  is 
produced  on  a  large  scale,  and  in  furnaces  of  considerable 
capacity,  it  is  best  to  drop  the  "  steep  "  crucible  entirely,  as 
the  large  volume  of  hot  metal  will  permit  the  use  of  the  much 
preferable  brick  "  well "  without  chilling.  In  either  case,  the 
furnace  should  be  taken  in  hand  by  the  head  smelter  as  soon 
as  the  water-jacketed  shell  is  properly  suspended  in  position 
with  its  upper  brick-work  complete,  and  the  connection  estab- 
lished between  the  same  and  the  stack  that  is  to  convey  away 
its  gases. 

If  the  furnace  is  to  be  used  for  matte  concentration  or  for  the 
production  of  pig-copper  from  roasted  matte,  and  consequently 
provided  with  a  steep  crucible,  four  iron  plates  should  be  pro- 
vided, forming  a  rectangular  box  about  3J  feet  high,  some  4 
inches  wider  than  the  furnace  on  each  side,  and  extending 
from  the  back  to  36  inches  in  front  of  the  breast.  The  front 
plate  is  provided  with  the  usual  cast-iron  slag-spout,  fitted  with 
a  groove  to  slip  on  without  bolts,  while  one  side  plate  should 
be  perforated  with  a  small  hole  or,  better,  slit,  two  inches  wide 
and  seven  inches  high.  As  this  is  the  tap-hole,  ifcs  lowest  point 
should  correspond  with  the  apex  of  the  inverted  cone-shaped 
crucible.* 

A  heavy  matte-spout,  eight  inches  long,  and  at  least  two 
inches  thick  on  the  bottom,  and  cast  as  part  of  a  strong  square 

*  The  cuts  accompanying  the  description  of  the  Herreshoff  and  Orford  fur- 
naces may  be  referred  to  in  connection  with  this  and  succeeding  paragraphs. 


182     MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

plate,  should  be  bolted  on  at  the  lower  edge  of  the  opening,  an 
arrangement  found  necessary  for  the  proper  and  efficient  plug- 
ging of  the  tap-hole.  A  foundation  for  this  iron  box,  which  is 
held  together  by  bolts  through  ears  or  other  simple  means, 
should  be  made  by  either  laying  down  thick  iron  plates  of  the 
proper  dimensions,  or  by  putting  in  a  tight  floor  of  fire-brick  on 
end,  laid  in  thin  clay  mortar  with  an  addition  of  10  per  cent,  of 
silicate  of  soda.  This  will  prevent  the  gradual  penetration  of 
matte  into  the  rock  foundation,  and  is  a  necessary  precaution. 
Upon  this,  the  portion  of  the  rectangle  corresponding  to  the 
base  of  the  furnace  is  built  up  as  a  solid  column  of  fire-brick  to 
within  10  or  12  inches  of  the  tuyeres. 

In  some  furnaces,  the  water-jacket  is  continued  for  a  con- 
siderable distance  below  the  tuyeres.  In  any  case  it  is  proper 
to  continue  the  brick-work,  on  the  outside  at  least,  to  the  edge 
of  the  jacket,  surrounding  the  lower  portion  of  the  latter  with 
a  few  courses,  to  insure  a  tight  joint. 

In  the  anterior  half  of  the  iron  fore-hearth,  a  single  row — 
4J  inches — of  fire-brick  is  sufficient  on  the  sides,  while  a  9-inch 
wall  is  usually  built  in  front,  an  elongated  opening  correspond- 
ing to  the  tap-hole  being  left  in  the  brick-work. 

It  is  now  evident  that  the  fore-hearth  is  filled  in  its  poste- 
rior half  with  a  solid  mass  of  brick-work,  extending  up  to,  and 
becoming  continuous  with,  the  circular  shell  of  the  furnace 
proper,  while  the  anterior  half  contains  a  large  square  opening, 
surrounded  by  a  brick  wall,  extending  down  nearly  to  the  foun- 
dation of  the  structure ;  communicating  by  a  channel  under  the 
breast  with  the  interior  of  the  furnace ;  opening  into  the  tap- 
hole  on  one  side,  and  into  the  slag-spout  in  its  upper  anterior 
wall. 

The  interior  of  the  furnace  is  now  provided  with  a  bottom, 
consisting  of  four  parts  ground  calcined  quartz  to  one  part  plas- 
tic fire-clay.  This  is  firmly  tamped  upon  the  brick  base  and 
carried  in  a  wedge-shaped  wall  around  the  sides  of  the  circular 
interior,  resting  against  the  water-jacket,  and  thinning  out  to 
nothing  just  below  the  tuyere  openings.  The  component  parts 
of  this  mixture  should  be  ground  through  a  16-mesh  screen,  or 
finer,  and  after  a  thorough  mixing,  should  be  slightly  moistened, 
and  tamped  firmly  into  place  with  iron  bars,  shaped  on  the  end 


THE  SMELTING  OF  COPPER.  183 

like  a  four-leafed  clover,  and  slightly  heated,  to  prevent  adhe- 
sion of  the  material. 

A  layer  of  three  or  four  inches  is  quite  sufficient  for  an  or- 
dinary furnace  bottom,  it  being  only  necessary  to  protect  the 
brick-work  until  there  is  deposited  from  the  smelting  charge  an 
exceedingly  refractory  mixture  of  metallic  iron,  matte,  and  slag, 
which  forms  a  massive  and  permanent  bottom,  far  superior  to 
any  artificial  substance.  It  is  only  in  smelting  very  poor  pyri- 
tous  ores,  producing  a  large  quantity  of  low-grade  matte,  that 
any  "  cutting  down  "  of  the  bottom  occurs.  The  measures  ap- 
propriate to  this  condition  of  things  will  be  discussed  when 
treating  of  the  large  brick  furnaces,  in  which  this  class  of 
material  is  commonly  produced. 

The  furnace  bottom  should  slope  slightly  toward  the  breast, 
at  which  point  it  meets  the  "  steep  "  (German,  Gestubbe  /  French, 
Brasque)  with  which  the  anterior  compartment  is  filled,  and  in 
which  the  crucible  is  formed,  its  deepest  point  communicating 
with  the  tap-hole  in  the  side  plate. 

This  moderate  and  economical  use  of  steep  must  not  be 
confounded  with  the  old-fashioned  practice  of  establishing  an 
enormous  fore-hearth,  filled  with  this  material,  and  requiring 
constant  repairs  and  attention.  Although  abolished  in  many 
modern  works,  it  possesses  peculiar  qualities,  which  render  it 
very  valuable  in  certain  blast-furnace  operations — such  as  the 
smelting  of  calcined  matte — where  the  product  is  either  pig- 
copper  or  a  very  high-grade  matte,  and  the  capacity  of  the 
furnace  not  large. 

Both  of  these  substances  have  a  strong  tendency  to  chill, 
especially  when  using  the  exterior  crucible,  which  is  for  the 
most  part  prevented  by  the  use  of  steep,  which,  besides  being 
an  excellent  non-conductor,  seems  actually  to  generate  heat — 
possibly  from  the  slow  combustion  of  its  carbon — thus  preserv- 
ing the  metal  fluid,  while  any  chill  that  may  form  in  the  cruci- 
ble is  easily  removed  without  damaging  its  walls  and  interior, 
as  would  be  the  case  with  clay  or  brick-work. 

The  permanency  of  the  basin  and  tap-hole  depends  greatly 
upon  the  quality  of  the  steep,  which  should  be  made  as  fol- 
lows :  Crush  the  constituents  separately  through  a  20-mesh 
screen,  or  as  much  finer  as  is  practicable.  A  Bogardus  or 


184      MODEKN  AMEEICAN   METHODS   OF   COPPER  SMELTING. 

Sturtevant  mill  will  be  found  useful  for  this  purpose,  and  has 
a  much  greater  capacity  than  the  light  stamps  often  used.  Mix 
very  thoroughly  while  dry,  and  moisten  with  water  through  a 
rose  nozzle  to  such  a  degree  that  the  mass  will  ball  when 
pressed  vigorously  in  the  hand,  without  imparting  any  damp- 
ness to  the  skin.  Tamp  firmly  with  inch  square  bars,  and 
avoid  stratification  by  adding  a  shovelful  at  frequent  intervals, 
and  before  a  hard  surface  is  produced  by  the  pounding.  The 
following  proportions  are  suitable  for  varying  conditions.  When 
the  product  is  metallic  copper,  use  by  measure  :  3  parts  coke, 
2  parts  raw^fire-clay  ;  or  4  parts  coke,  2  parts  raw  clay,  1  part 
burnt  clay  or  ground  brick ;  or  3  parts  charcoal-dust,  2  parts 
raw  clay,  1  part  ground  red  brick.  For  a  product  of  rich  matte, 
use :  7  parts  coke,  5  parts  raw  clay ;  or  3  parts  charcoal,  2 
parts  raw  clay,  1  part  burnt  red  brick. 

A  large  proportion  of  carbon  counteracts  the  chilling  of  the 
metal  and  the  consequent  formation  of  skulls  in  the  fore-hearth, 
but  is  less  able  to  stand  mechanical  violence  than  the  heavier 
steep,  which  has  more  plasticity.  Charcoal-dust  makes  a  some- 
what fragile  mixture,  but  an  excellent  one  for  retaining  heat. 

The  arrangement  just  described  is  particularly  suited  to  a 
small  slow-running  furnace,  where  it  is  intended  to  make  a 
rich  product,  and  where  reasons  exist  for  producing  a  slag  suf- 
ficiently free  from  copper  to  be  at  once  rejected.  That  this  is 
perfectly  practicable  is  demonstrated  at  various  establishments 
in  this  country,  where,  by  a  somewhat  lavish  expenditure  of 
fuel,  a  light  blast,  and  a  very  slow  run,  a  slag  containing  below 
O7  per  cent,  of  copper  and  exceedingly  ferruginous  is  produced 
in  conjunction  with  pig-copper.  The  material  smelted  is  stall- 
roasted  matte,  with  a  very  small  addition  of  old  brick  and  fur- 
nace ends,  and  in  spite  of  the  character  of  the  charge  and  the 
powerful  reducing  action  due  to  the  slow  run,  the  formation  of 
all  metallic  iron  is  avoided — a  result  almost  impossible  to  ob- 
tain in  furnaces  with  an  interior  crucible.* 

*  The  best  example  of  this  interesting  but  somewhat  antiquated  practice, 
though  executed  in  brick  furnaces,  is  found  at  Ely,  Vermont,  where  there 
are  some  eight  furnaces  for  the  production  of  pig-copper  in  the  manner  indi- 
cated. Owing  to  legal  difficulties?,  the  works  are  not  now  in  active  opera- 
tion. 


THE   SMELTING  OF   COPPER.  185 

To  prevent  the  delay  arising  from  the  frequent  though 
slight  repairs  indispensable  from  this  form  of  furnace,  it  is 
sometimes  customary  to  widen  the  fore-hearth  sufficiently  to 
contain  two  crucibles  side  by  side  and  used  alternately. 

The  copper  may  be  removed  from  the  crucible  either  by 
tapping  into  molds  of  sand  or  iron,  or  by  ladling,  the  latter 
method  being  more  frequently  employed  where  the  product  is 
pig-copper,  owing  to  the  difficulty  of  opening  the  tap-hole  after 
a  run  of  some  length.  For  ordinary  ore-smelting,  producing  a 
matte  below  50  per  cent,  copper — usually  between  33  and  40  per 
cent. — no  arrangement  can  approach  the  modern  brick  fore- 
hearth  for  convenience,  economy,  and  safety ;  nor  can  the  solid 
brick  base  just  described  compare  with  the  simple  iron  drop 
bottom,  as  used  in  cupolas  devoted  to  the  melting  of  pig-iron 
or  castings.  A  most  useful  modification  of  this  fore-hearth  is 
shown  in  the  illustrations  of  the  Herreshoff  furnace.  The  pro- 
fession is  indebted  to  Mr.  J.  B.  F.  Herreshoff  for  this  as  well 
as  for  several  other  improvements  in  connection  with  this  fur- 
nace. The  author  also  desires  to  express  his  obligations  to  the 
same  gentleman  for  many  valuable  practical  suggestions  that 
he  will  not  attempt  to  specify  in  detail.  The  fore-hearth  or 
"well"  is  here  placed  on  wheels,  for  convenience  of  removal, 
though  more  frequently  it  rests  upon  the  solid  ground. 

Another  feature  of  especial  value  is  the  arrangement  of  the 
bottom  of  this  furnace,  which  consists  merely  of  a  circular,  con- 
cave cast-iron  plate,  firmly  bolted  to  the  lower  border  of  the 
water-jacket,  which  extends  some  twelve  inches  below  the 
tuyeres.  This  bottom  is  covered  with  a  single  course  of  fire- 
brick, resting  on  a  shallow  layer  of  sand,  and  might  seem  to  be 
but  a  feeble  barrier  to  such  material  as  molten  ore.  It  would, 
in  fact,  last  but  a  very  short  time,  were  it  not  that  the  outlet 
of  the  furnace,  through  which  all  its  liquid  contents  must  pass, 
consists  of  a  4-inch  by  7-inch  circular  opening  through  one  side 
of  the  water-jacket,  and  is  consequently  so  protected  that  the 
slag  and  matte  can  cut  their  way  no  deeper  than  the  lower  rim 
of  the  opening.  There  stands,  therefore,  constantly  within  the 
furnace  a  pool  of  molten  material  at  least  as  deep  as  the  lower 
border  of  the  orifice  referred  to,  while  the  constant  loss  of  heat 
therefrom  by  radiation  through  the  thin  bottom  of  the  furnace 


186     MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

speedily  converts  it  into  a  solid  and  permanent  block,  which 
need  only  be  removed  when  cause  exists  for  detaching  the  bot- 
tom. The  most  novel  feature  of  this  arrangement  consists  in  a 
similar  opening  in  the  back  wall  of  the  movable  fore-hearth, 
which,  being  also  protected  by  a  small  separate  water-jacket 
plate,  and  backed  up  until  it  exactly  meets  the  furnace  opening, 
forms  a  continuous,  though  very  short,  water-cooled  channel 
from  furnace  to  fore-hearth.  The  slag  discharge  of  the  latter 
is  several  inches  higher  than  this  channel,  so  that  when  the 


HERRESHOFF  NEW  FURNACE. 


well  is  full  and  slag  begins  to  run  over  into  the  pots,  the  opening 
just  described  is  covered  several  inches  deep  with  liquid  mate- 
rial, which  stands  at  the  same  depth  in  the  interior  of  the  fur- 
nace as  in  the  fore-hearth,  except  in  so  far  as  lowered  by  the 
pressure  of  the  blast.  The  wind  is  thus  completely  trapped, 
and  its  constant  blowing  through,  which  is  one  of  the  most 
common  and  obstinate  annoyances  of  blast-furnace  practice, 
is  effectually  prevented. 


THE  SMELTING  OF  COPPER. 


187 


The  products  of  the  fusion,  usually  only  two  in  number  in 
copper  smelting,  separate  in  this  large  fore-hearth  very  com- 
pletely, the  matte  settling  quietly  to  the  bottom,  while  the  slag 
flows  through  the  anterior  spout  in  a  constant  stream.  When 
globules  of  matte  begin  to  appear  in  the  slag  stream,  as  evinced 
by  the  sparkling  of  the  same  while  falling  into  the  pot,  and  its 
greater  liquidity  when  a  small  portion  of  the  suspected  slag  is 
caught  in  a  shovel  and  inclined  from  side  to  side  while  cooling, 


W 


HEKKESIIOFF  NEW   FURNACE. 


the  tap-hole  in  the  side  plate  is  opened  with  a  pointed  steel  bar, 
driven  in  with  a  heavy  hammer  if  necessary,  and  the  metal  al- 
lowed to  flow  into  molds  of  sand  or,  in  some  cases,  of  cast-iron. 
When  the  well  is  thus  empty  and  the  communicating  chan- 
nel between  furnace  and  fore-hearth  uncovered,  the  blast  es- 
capes through  the  same  with  full  force,  chilling  the  surface  of 
the  slag  in  its  passage,  and  hurling  glowing  fragments  of  coke 
and  globules  of  molten  ore  in  every  direction.  This  is  com- 
pletely obviated  in  the  Herreshoff  system  by  plugging  the  slag- 
spout  opening  with  a  ball  of  plastic  clay  heavily  weighted.  The 


188     MODEKN  AMERICAN   METHODS   OF   COPPER   SMELTING. 

fore-hearth  being  tightly  covered  with  slabs  formed  of  fire-brick 
held  together  by  iron  clamps,  the  blast  is  in  this  way  entirely 
confined  to  the  interior  of  the  furnace,  while  the  fore-hearth 
soon  fills,  and  the  wind  is  trapped  as  before. 

Still  another  convenient  feature  is  shown  in  the  arrangement 
by  which  the  matte,  when  tapped,  is  kept  free  from  the  after- 
coming  slag,  of  which  a  considerable  quantity  is  present  in  the 
interior  of  the  furnace  and  well,  even  after  the  appearance  of 
matte  at  the  slag-spout.  As  it  is  sometimes  impossible  or  un- 
advisable  to  close  the  tap-hole  at  the  exact  moment  when  the 
last  of  the  matte  has  escaped  and  the  first  of  the  slag  begins  to 
flow,  Mr.  Herreshoff  has  arranged  a  tilting  iron  launder  between 
the  matte-spout  and  molds,  which,  when  held  up  by  a  chain 
passing  over  a  pulley,  conducts  the  liquid  to  the  regular  molds> 
but  when  released  by  a  catch,  turns  upon  a  horizontal  pivot,  and 
conveys  the  slag  in  the  opposite  direction  and  into  compart- 
ments in  the  sand,  where  it  is  obtained  in  proper  shape  for 
re-smelting. 

Brick  fore-hearths  of  various  patterns,  but  in  the  main  resem- 
bling the  type  just  described,  have  been  in  use  in  smelting  sul- 
phide copper  ores  for  some  seven  or  eight  years,  and  are  cer- 
tainly superseding  all  other  arrangements.  A  brick  fore-hearth 
of  this  description,  strengthened  by  iron  plates  cast  dishing  to 
prevent  cracking,  and  firmly  bolted  together  through  projec- 
tions at  the  corners,  will  last,  according  to  the  quality  of  the  pro- 
ducts and  the  rapidity  of  the  process,  for  from  two  to  thirty 
days,  a  week  being  perhaps  the  average  life.  Their  destruc- 
tion is  brought  about  in  two  ways :  by  gradual  chilling  about 
the  sides  and  bottom  until  the  cavity  becomes  too  small  or  tap- 
ping is  rendered  impossible  ;  or  by  the  cutting  away  of  the  brick 
lining  from  the  action  of  a  hot  basic  slag  and  a  low-grade  ferru- 
ginous matte.  The  former  condition  results  usually  from  the 
presence  of  a  siliceous,  infusible  slag,  especially  when  accom- 
panied by  a  matte  of  high  grade,  which,  from  its  high  conduct- 
ing qualities,  has  a  strong  tendency  to  chill.  It  is  also  espe- 
cially influenced  by  the  rapidity  of  the  smelting  process,  a 
quick  run  with  a  large  stream  of  hot  slag  and  metal  keeping  a 
basin  open  where  the  fusion  of  only  half  the  amount  in  the 
same  time  would  chill  it  within  a  few  hours.  Any  long  stoppage 


THE   SMELTING  OF  COPPER.  189 

is  particularly  detrimental,  and  may  spoil  a  new  basin  within 
the  first  few  hours. 

Even  under  the  most  favorable  conditions  possible,  a  cer- 
tain minimum  capacity,  about  20  tons  in  twenty-four  hours, 
seems  absolutely  essential  to  the  employment  of  the  brick  fore- 
hearth,  and  this  minimum  only  if  the  matte  is  tolerably  low 
grade — below  36  per  cent.  As  this  amount  can  usually  be 
treated  even  in  the  smallest  furnace  likely  to  be  erected,  the 
conditions  that  forbid  the  employment  of  the  brick  fore-hearth 
do  not  often  occur  in  the  smelting  of  sulphide  ores. 

While  the  "  chilling  up"  or  "  cutting  out  "  of  the  old  form 
of  crucible  in  the  interior  of  the  furnace  involved  a  costly  and 
tedious  series  of  operations,  comprising  the  blowing  out  and 
cooling  down  of  the  furnace,  the  exterior  basin  can  be  taken 
down,  replaced,  and  dried  ready  for  work  within  a  few  hours  ; 
and  it  is  here  that  the  advantages  of  this  method  of  practice  be- 
come most  apparent,  as  the  stoppage  of  the  blast  for  this  short 
period  causes  little  or  no  trouble  in  the  furnace  itself.  The 
arrangement  of  the  fore-hearth  on  wheels  is  a  notable  conven- 
ience, as  the  exchange  can  be  made  with  great  facility,  and  the 
new  basin,  heated  to  redness  by  a  coke  fire,  is  pushed  into  place 
between  the  two  guiding  rails,  a  gasket  of  clay  being  interposed 
between  the  respective  abutting  faces,  to  prevent  the  leakage  of 
the  liquid  product.  As  soon  as  the  connection  is  made  between 
the  main  pipe  and  the  diminutive  jacket  on  the  back  plate  of  the 
fore-hearth,  the  clay  plug  with  which  the  main  orifice  into  the 
furnace  was  closed  is  pierced,  and  the  process  goes  on  with  the 
slightest  possible  delay.* 

After  cooling  the  interior  of  the  old  fore-hearth  with  water, 
the  iron  plates  are  removed  and  the  chilled  mass  broken  into 
fragments  for  resmelting. 

The  chill  usually  consists  of  a  mixture  of  slag  and  matte, 
and  is  seldom  so  difficult  to  handle  as  to  require  the  aid  of 
blasting  powder.  This  condition,  when  present,  usually  results 
from  the  deposition  of  metallic  iron,  which  is  sometimes  found 
several  inches  thick  and  in  a  fine-grained,  massive  condition. 

*  The  time  consumed  in  tlie  above  operation,  as  taken  twice  under  ordi- 
nary circumstances,  was  18  and  21  minutes. 


190    "MODERN  AMERICAN  METHODS  OF  COPPER  SMELTING. 


It  is  best  treated  by  exploding  a  cartridge  of  the  strongest 
Giant  powder  upon  it,  though  drilling  is  sometimes  necessary. 
A  ratchet-drill  is  used  for  the  purpose,  and  a  sample  of  borings 
from  such  a  chill,  analyzed  for  the  writer  by  Mr.  A.  F.  Glover, 
Ph.D.,  had  the  following  composition : 


Sulphur 4-64 

Copper 9-80 

iron 82-70 

Carbon 1-12 

Arsenic..  0'41 


Slag 0-78 

Nickel  and  cobalt 0'81 

99-96 


This  substance  may  be  felt  as  a  sticky,  glutinous,  semi-fused 
mass  in  the  bottom  of  the  basin,  and  is  often  scraped  out  in  con- 
siderable quantities  after  tapping.  The  life  of  the  basin  is  also 
often  prolonged  by  a  systematic  chiseling  out  of  the  sides,  front, 
and  bottom,  whenever  empty,  and  a  careful  and  energetic  fur- 
nace-man will  keep  his  fore-hearth  in  condition  for  an  extraor- 
dinary period. 

The  chilling  of  the  basin  is  counteracted  by  anything  that 
checks  the  radiation  of  heat  therefrom,  and  a  backing  of  two 
inches  of  asbestos  between  the  brick  lining  and  iron  plates  is 
reported  by  Mr.  Herreshoff  to  effect  good  results.  The  writer 
has  used  a  mixture  of  wood  ashes  and  crushed  porous  slag 
with  good  effect.  The  size  of  the  basin  varies  according  to  the 
conditions  of  the  case  and  the  fancy  of  the  metallurgist.  A 
rectangle  of  28  by  30  inches  and  28  inches  deep  will  be  found 
convenient.  It  should  contain  from  one  to  two  tons  of  matte, 
and  when  inclined  to  chill,  should  be  made  larger  at  the  com- 
mencement than  under  contrary  conditions. 

The  amount  of  ore  treated  in  water-jacket  furnaces  of  the 
same  size  and  with  exterior  basin  differs  greatly,  according  to 
its  fusibility,  the  quality  of  fuel,  and  numerous  local  conditions. 
A  few  examples  from  practice  will  assist  in  forming  an  estimate. 

Herreshoff 's  first  water-jacket  at  the  Laurel  Hill  Chemical 
Works,  Long  Island  City,  is  shown  in  the  accompanying  illus- 
trations. 

Wendt  says :  "  In  front  of  the  water-jacket  A,  the  fore- 
hearth  B  is  placed  on  wheels,  and  can  be  readily  removed  from 
the  front  of  the  furnace.  The  molten  material  flows  directly 
from  the  shaft  through  the  opening  E  into  the  fore-hearth. 


THE   SMELTING   OF   COPPER. 


191 


The  joint  between  (lie  two  is  readily  made  or  severed  ;  for  it 
consists  simply  of  two  water-jacketed  faces  of  iron,  which  are 
placed  in  contact  by  moving  the  fore-hearth  B  against  the 
jacket  A.  The  cooled  iron  surfaces  immediately  chill  any 
matte  or  slag  liable  to  run  between  them,  and  make  a  perfect 
joint  between  furnace  and  fore-hearth.  The  first  furnace 
erected  was  round,  and  48  inches  in  diameter.  Figs.  29  and  30 
illustrate  its  construction. 

The  water-jacket  A  rests  on  four  posts  attached  to  the  bot- 


tom by  brackets,  as  shown  in  the  cut.  C  is  fire-clay  rammed 
into  the  bottom  on  a  supporting  cast-iron  plate,  fastened  to  the 
furnace  ;  D  is  the  wind-box ;  H  the  entrance  of  cooling  water  ; 
/  the  exit  of  same ;  0  the  charging-door ;  B  the  rectangular 
fore-hearth  with  fire-brick  sides,  top,  and  bottom,  held  by  an 
iron  plate-casing;  K  a  layer  of  slag;  T^the  cinder-lip;  and 
G  the  tap-hole  for  the  matte  in  the  fore-hearth.  The  second 


192     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

furnace,  built  at  the  Laurel  Hill  Works,  was  of  the  same  circu- 
lar shape,  but  60  inches  diameter.  Blast  was  furnished  at  the 
usual  low  pressure  by  a  Baker  blower,  and  trouble  was  experi- 
enced by  the  failure  of  the  blast  to  reach  the  center  of  the 
furnace. 

The  last  furnace  erected,  and  the  one  now  in  use,  shown  in 
Figures  31,  32,  and  33,  is  rectangular  in  shape,  with  corners 
rounded,  and  the  lines  between  the  corners  slightly  curved  or 
of  convex  shape.  The  height  is  ten  feet,  width  3  feet  7 
inches  at  the  bottom,  and  4  feet  7  inches  at  the  top,  by  6  feet  4 
inches  length  at  the  bottom,  and  7  feet  4  inches  at  the  top. 
The  water-jacket  is  exceptionally  narrow,  having  a  water-space 
of  only  2  inches. 

Keferiring  to  the  cuts,  A  is  the  body  of  the  furnace ;  B  a 
ring  2  by  2  inches,  to  which  the  plates  of  the  water-jacket  are 
riveted.  At  the  top  (7,  the  outer  plate  is  flanged  2  inches,  and 
the  inner  plate  4  inches,  and  the  flanges  then  riveted.  The 
bottom  of  the  furnace  E  is  a  disked  cast-iron  plate  1J  inches 
thick,  fastened  to  the  ring  B  by  tap-bolts.  This  permits  the 
dropping  of  the  bottom  if  required.  The  legs  F  are  bolted  to 
the  ring  B  on  the  outside  of  the  furnace,  thus  not  interfering 
with  the  dropping  of  the  bottom.  The  hole  G  is  the  outlet  of 
the  furnace  for  both  slag  and  matte.  It  is  9  inches  high  and  7 
inches  wide,  and  made  by  riveting  the  wrought-iron  frame  H 
into  the  shell  of  the  furnace.  The  furnace  is  blown  by  13 
tuyeres,  five  on  each  side  and  three  on  the  back.  They  are 
placed  26  inches  above  bottom  plate,  and  are  two  inches  in 
diameter. 

The  construction  of  the  furnace  proper  is  practically  iden- 
tical with  that  of  the  original  round  furnace,  but  the  fore-hearth 
is  considerably  changed.  In  the  round  furnace  (see  Fig.  29), 
the  fore-hearth  was  floored  with  a  layer  of  slag-wool  and  brick 
as  described.  A  brick  lining  was  also  used.  The  bottom  of 
the  brick  lining  was  some  12  inches  below  the  outlet  from  the 
jacket.  Experience  proved  that  this  bottom  invariably  chilled 
to  a  level  with  the  bottom  of  the  opening  to  the  furnace.  The 
cutting  of  the  brick  lining  at  a  higher  level  also  gave  occasional 
trouble.  Both  these  faults  are  avoided  in  the  present  con- 
struction. The  former,  by  raising  the  fore-hearth  on  high 


THE   SMELTING  OF  COPPER.  193 

wheels  N,  and  making  the  floor  of  the  bottom  lining  within  2 
inches  of  a  level  with  the  bottom  of  the  inlet  L.  The  latter, 
by  entirely  casting  aside  fire-brick  lining  and  depending  on  the 
circular  cast-iron  water-jacket  K.  The  tap-hole  R  in  the  shaft 
of  the  furnace  is  used  only  when  blowing  out  to  tap  the  furnace 
clean,  or,  sometimes,  for  such  small  quantities  of  black  copper 
as  may  be  accidentally  made.  In  the  fore-hearth,  the  tap-hole 
0  is  the  one  commonly  in  use.  It  is  made  of  copper,  bolted 
to  the  iron  body  of  the  fore-hearth,  and  is  water-jacketed 
similarly  to  the  "  Liirmann  "  slag  tuyere  of  iron  furnaces.  The 
manner  of  operating  it  is  also  similar.  M  is  the  slag-spout ; 
W,  a  brick-lined,  dish-shaped  movable  iron  cover  of  the  fore- 
hearth.  When  smelting,  the  well  or  fore-hearth  is  wheeled  up 
against  the  furnace,  as  shown  in  the  cut,  and  a  very  small 
amount  of  wet  fire-clay  is  placed  on  the  iron  faces  surrounding 
the  holes  G  and  L,  in  order  to  make  a  tight  joint  between  them. 
In  practical  operation,  after  the  furnace  has  been  properly 
charged,  the  blast  is  let  on.  The  first  cinder  collects  in  the 
bottom  of  the  furnace  shaft  proper,  and  accumulates  until  it 
reaches  the  holes  G  and  L.  It  then  overflows  rapidly  into  the 
fore-hearth,  carrying  matte  with  it.  In  a  short  time,  the  level 
of  the  molten  material  rises  above  the  top  of  the  hole  L,  and 
from  that  time  onward  the  blast  in  the  furnace  can  no  longer 
blow  out  through  Z,  and  is  completely  trapped.  Owing  to  the 
pressure  of  blast,  the  level  of  molten  matte  and  slag  in  the  fore- 
hearth  is  several  inches  above  that  in  the  furnace  proper. 
Eventually  the  slag-lip  M  is  reached  by  the  cinder,  which  then 
overflows  quietly.  Matte  is  tapped  periodically  from  the  tap- 
ping-notch 0  without  stopping  the  furnace.  Matte  is  never 
allowed  to  accumulate  until  it  overflows  at  the  slag-lip,  the 
practice  being  to  tap  at  stated  intervals.  The  notch  0  is 
opened  by  a  small  steel  bar,  and  pure  matte,  to  the  amount  of 
about  1,000  pounds,  is  allowed  to  run  off.  During  this  operation, 
the  level  of  the  molten  slag  in  the  fore-hearth  falls,  but  not  suf- 
ficiently to  admit  of  blast  escaping  through  L.  By  the  simple 
insertion  of  a  small  clay  stopper,  the  matte  is  stopped  before 
cinder  appears,  thus  avoiding  all  cinder  picking.  The  whole 
process  only  occupies  a  few  minutes,  and  is  so  perfect  that  for 
months  a  miss  in  tapping  or  closing  up  has  not  been  made. 
13 


194     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

The  large  amount  of  molten  slag  and  metal  in  the  fore- 
hearth  greatly  facilitates  a  clean  separation,  as  the  slag  analysis 
clearly  shows.  The  high  percentage  of  the  matte,  made  with- 
out trouble  from  ironing,  is  entirely  due  to  the  great  rapidity 
of  the  smelting.  Standing  at  the  charging-floor,  the  charge 
sinks  visibly  while  watching  it,  and  is  exposed  so  short  a  time 
to  the  action  of  reducing  gases  that  the  iron  is  slagged  before 
reduction,  and  thus  ceases  to  be  the  obstacle  to  a  rapid  con- 
centration of  copper  in  a  high-grade  matte  that  metallurgists 
usually  consider  it. 

The  following  data  of  work,  done  by  the  different  sizes  of 
furnaces,  speak  for  themselves.  The  saving  in  fuel  by  the 
larger  furnaces  is  apparent : 

AVEBAGE  CHARGE  PER  DIEM. 

48-inch  furnace.  60-inch  round  furnace.  Rectangular  furnace. 
Roasted  ore.  .51 '7  tons.  76 '0  tons.  76 '8  tons. 

Raw  fines....  4'3    "  8'0     "  13'2     " 

Sand 2-8    "  12'0     "  5'3     " 

Iron  slag 9-5"  


Total  stock,  58 -8    "  105 '5     "  95'3 


Coke 11 '5  tons  or  20  pr.  ct.  17'0tonsorl6pr.  ct.  17*4  tons  or  18  pr.ct. 

The  cost  of  smelting  in  the  large  Herreshoff  furnace  is  very 
low.  The  total  employes  per  diem  are  ten  men,  and  with  gas- 
house  coke  at  $2.50  a  ton,  and  repairs  exceptionally  low,  the 
total  cost  per  ton  of  ore  cannot  aggregate  80  cents,  or,  on  the 
ton  of  50  per  cent,  matte,  about  $10 ;  or  1  cent  per  pound  of 
copper  contained. 

A  42-inch  jacket  with  five  tuyeres  and  half-pound  blast  at 
Stratford,  Yermont,  smelts  from  40  to  45  tons  of  roasted 
pyritous  ore,  which  yields  a  monosilicate  slag  and  a  matte 
averaging  30  per  cent,  copper. 

The  42-inch  water-jacket  of  the  late  Chemical  Copper  Com- 
pany at  Phoenixville,  Pa.,  with  tuyeres  and  blast  as  in  last 
example,  smelted  from  35  to  50  tons  daily,  according  to  the 
character  of  the  charge. 

In  Butte  City,  Montana,  a  48-inch  wrought-iron  jacket,  with 
six  2-inch  tuyeres  and  five-eighths  of  a  pound  blast,  smelted 
from  60  to  65  tons  daily  of  calcined  pyritic  concentrates,  largely 


THE   SMELTING  OF  COFFEE.  195 

in  a  fine  condition.  In  this  instance,  tlie  richness  of  the  ore, 
combined  with  a  quite  thorough  calcination,  gave  such  a  high 
grade  of  matte  as  to  render  the  employment  of  an  external 
fore-hearth  an  impossibility,  in  consequence  of  the  rapid  chill- 
ing of  the  metal,  which  soon  closed  the  tap-hole  effectually, 
and  in  thirty-six  hours  reduced  the  basin  to  too  small  a  size, 
which  difficulty  has  been  obviated  by  substituting  an  "  Orford  " 
fore-hearth,  with  automatic  tap,  to  be  described  later. 

These  are  average  results,  the  fuel  in  all  cases  being  coke 
of  good  quality,  with  from  12  to  15  per  cent,  ash,  and  the  ores 
rather  basic  than  siliceous.  The  performance  of  the  same  type 
of  furnaces  when  producing  pig-copper  from  oxidized  ores  will 
be  noticed  later. 

By  inexperienced  metallurgists,  the  general  construction 
and  arrangement  of  the  water-jacket  furnace  may  safely  be  left 
to  the  manufacturers,  several  of  whom  have  had  a  wide  experi- 
ence in  this  matter.  The  quality  of  the  material  to  be  used  has 
already  been  noticed,  nor  is  it  good  management  to  economize 
in  this  particular. 

The  water-jackets  are  usually  made  from  sheets  of  iron 
or  steel,  rolled  to  the  proper  size,  to  avoid  unnecessary  rivet- 
ing, and  the  rivet-heads  on  the  inside  of  the  shaft  should  pro- 
ject as  little  as  possible,  to  avoid  burning  off. 

The  closing  in  of  the  water-space  at  top  and  bottom  is 
effected  by  bending  over  and  riveting  the  sheets  together,  or 
better,  by  the  introduction  of  a  circular  ring  of  2-inch  square 
wrought-iron,  forming  a  solid  frame,  through  which  the  rivets 
pass,  holding  the  iron  plates  firmly  in  place.  A  similar  ar- 
rangement of  cast  blocks  is  provided  for  the  tuyere  openings  ; 
the  castings  having  a  central  orifice  of  the  proper  size  for  the 
tuyere  and  a  circular  row  of  perforations  for  the  passage  of  the 
rivets.  The  tuyere  openings  are  usually  equally  spaced,  and 
from  18  to  20  inches  from  center  to  center. 

A  convenient  arrangement  for  the  distribution  of  the  wind 
consists  in  a  cast-iron  wind-box  surrounding  the  furnace  and 
in  air-tight  communication  with  the  tuyere  openings,  the  blast 
entering  the  former  from  the  main  wind-pipe.  In  the  Herres- 
hoff  furnace,  the  tuyeres  are  rendered  easily  accessible  by  a 
circular  hinged  plate  opposite  each,  and  provided  with  an  eye- 


196      MODEKN  AMERICAN  METHODS   OF   COPPEE  SMELTING. 

glass.  In  other  cases,  the  tuyeres  consist  merely  of  galvanized 
iron  pipes,  connected  with  properly  placed  branches  from  the 
circular  main  blast-pipe  surrounding  the  furnace,  though  inde- 
pendent of  the  latter.* 

The  connection  between  blast-pipe  and  tuyere-pipe  is 
usually  made  by  the  so-called  tuyere-bag,  consisting  merely 
of  a  light  duck  hose,  soaked  in  alum-water  to  render  it  unin- 
flammable and  impervious  to  the  wind. 

The  height  of  the  furnace  depends  on  the  quality  of  ore  and 
fuel,  as  well  as  the  nature  of  the  process ;  refractory,  siliceous 
ores,  and  dense,  strong  coke  or  charcoal  permitting  and  requir- 
ing the  employment  of  a  much  higher  furnace  than  the  op- 
posite conditions.  As  the  greater  number  of  water-jackets 
running  on  sulphide  ores  in  this  country  are  favored  with  a 
basic  and  easily  fusible  charge,  any  height  above  10  feet — from 
tuyeres  to  charge-door — is  rarely  met  with ;  and  even  when 
smelting  more  infusible  material,  the  danger  of  reducing  metal- 
lic iron  and  the  general  un  manage  ability  of  a  high  furnace 
would  render  of  doubtful  value  any  increase  of  the  height 
beyond  14  feet. 

The  arrangement  of  the  upper  portion  of  the  furnace  will 
depend  principally  upon  the  ultimate  disposal  of  the  smoke 
and  fumes.  The  simplest  and  cheapest  plan  consists  of  a 
strong  sheet-iron  stack,  lined  with  a  single  thickness  of  fire- 
brick, and  erected  upon  the  same  columns  that  support  the 
jacket  itself. 

Such  an  arrangement  could  hardly  be  permanent,  as  the 
flue-dust  from  any  material  worth  smelting  should  be  suffi- 
ciently valuable  to  pay  for  saving.  As  this  usually  involves  the 
leading  of  the  furnace  gases  down  to  the  level  of  the  ground, 
it  is  customary  to  effect  this  by  means  of  a  so-called  "  down- 
take,"  consisting  of  a  vertical  or  inclined  flue,  leading  from  the 
furnace  at  a  point  above  the  charging-door  to  the  entrance  of 
the  condensation-chambers  or  subterranean  flue  system. 

*  Professor  Richards,  of  the  Massachusetts  Institute  of  Technology,  has 
improved  on  the  above  by  the  use  of  an  ordinary  steam-pipe  of  the  proper 
size,  which  is  ground  slightly  tapering,  to  make  a  tight  joint  in  the  tuyere 
opening,  while  a  tee  at  the  opposite  end  provides  for  the  connection  with  the 
overhead  blast-pipe,  as  well  as  for  a  glass  eye-piece. 


THE   SMELTING  OF   COPPER.  197 

The  charging-door  should  be  proportionate  in  size  to  the 
furnace,  and  should  open  from  12  to  18  inches  above  the  charg- 
ing-platform,  to  insure  the  proper  feeding  of  the  furnace ;  for 
dishonest  laborers  find  it  more  convenient  merely  to  push  the 
ore  into  an  opening  level  with  the  floor  than  to  scatter  it  in 
the  careful  and  systematic  manner  so  essential  to  the  regular 
working  of  the  furnace. 

In  cases  where  the  occurrence  of  zinc-blende  or  even  galena 
in  the  ore  renders  the  formation  of  wall-accretions  a  matter  of 
probability,  it  will  greatly  facilitate  their  removal  to  have  the 
charging-door  in  the  sloping  roof- shaped  housings  above  the 
furnace  shaft,  as  long  bars  can  thus  be  introduced  with  ease. 
This  opening  should  be  provided  with  a  close-fitting  door,  and 
an  easy-working  iron  damper  should  be  placed  in  some  acces- 
sible part  of  the  chimney  or  down-take,  a  great  diminution  of 
flue-dust  being  observable  when  the  rapidity  of  the  chimney 
draught  is  so  checked  that  the  fumes  are  barely  carried  away. 

The  difference  is  obvious  between  the  conditions  in  cupola 
practice,  where  the  draught  merely  serves  to  remove  the  fumes 
produced,  while  the  combustion  results  entirely  from  the  blast 
below,  and  reverberatory  work,  where  the  burning  of  the  fuel, 
and  consequent  temperature,  depend  solely  on  the  draught 
produced  in  the  chimney. 

The  ordinary  shape  of  the  American  water-jacket  is  that 
of  the  frustum  of  an  inverted  cone  or  pyramid,  the  upper  diam- 
eter being  from  8  to  12  inches  greater  than  the  lower,  while 
the  use  of  boshes  is  very  rare,  owing  to  the  causes  already 
mentioned  as  influencing  the  height  of  ordinary  furnaces. 

A  slight  bosh  would  be  quite  in  place  in  smelting  refractory 
ores,  and  is  used  to  advantage  in  the  Bell  furnace  at  Butte 
City,  where  a  very  siliceous  charge  is  smelted  with  poor  char- 
coal. 

Where  condensation-chambers  or  long  flues  exist,  the  size 
of  the  chimney  seldom  stands  in  any  exact  relation  to  the  re- 
quirements of  a  single  cupola  ;  but  where  no  such  passages  are 
interposed,  any  data  of  the  capacity  of  stack  necessary  for  a 
furnace  of  a  given  size  are  useful,  especially  in  the  case  of  blast- 
furnaces, where,  owing  to  reasons  already  mentioned,  the  ordi- 
nary rules  governing  the  subject  cannot  be  applied. 


198     MODERN  AMERICAN  METHODS  OF  COPPER  SMELTING. 

For  a  single  circular  chimney,  either  directly  above  the 
jacket-shaft,  or  communicating  with  the  same  by  a  non-descend- 
ing flue,  experience  shows  that  the  ratio  between  the  diameter 
of  the  chimney  and  the  furnace  diameter  at  the  tuyeres  should 
be  about  as  2  to  3.  Thus,  a  36-inch  furnace  requires  a  24-inch 
stack ;  a  60-inch  furnace,  a  40-inch  stack,  etc.  * 

Any  considerable  lessening  of  this  ratio  is  likely  to  inter- 
fere with  the  draught  and  give  rise  to  an  annoying  and  injuri- 
ous escape  of  gas  from  the  charging-door. 

The  following  measurements  have  been  taken  from  stacks  in 
various  works  in  the  United  States,  being  selected  from  a  con- 
siderable number : 


Diameter  of  f  nrnace  at 
tuyeres,  in  inches. 

Diameter  of  stack, 
in  inches. 

Kesulting  draught. 

42 
40 
36 

48 
48 

30 
24 
20 
30 
36 

Excellent. 
Fair. 
Feeble. 
Feeble. 
Excellent. 

The  last  two  measurements  refer  to  the  same  furnace,  the 
draught  being  so  poor  with  the  smaller  chimney  as  to  require 
its  enlarging. 

While  an  elevation  of  a  few  feet  above  the  roof  is  sufficient 
to  carry  off  the  fumes,  safety  demands  that  cupola  stacks 
should  have  such  a  height  that,  during  the  blowing  in  and  out 
of  the  furnace,  the  sparks  and  burning  fragments  of  fuel  that 
are  then  projected  in  considerable  quantities  shall  be  carried 
to  a  proper  elevation. 

The  water-jacket  furnaces  employed  for  the  fusion  of  oxi- 
dized ores  do  not  differ  in  any  essential  particulars  from  those 
just  described.  Being  used  principally  in  Arizona,  New  Mex- 
ico, and  other  distant  parts  of  the  country,  where  mechanics' 
and  masons'  labor  as  well  as  fire-brick  and  similar  refractory 
materials  are  very  dear,  these  furnaces  are  so  arranged  as  to 

*  If  the  sizes  of  chimneys  here  given  seem  unnecessarily  large,  it  must  be 
remembered  that,  when  in  good  condition,  the  blast-furnace  is  so  cold  on  top 
as  to  permit  the  introduction  of  the  naked  hand,  and  consequently,  the  tem- 
perature of  the  column  of  air  in  the  stack  is  so  low  as  to  cause  but  little  dif- 
ference in  weight  between  the  interior  and  the  exterior. 


THE  SMELTING  OF   COPPER.  199 

be  almost  entirely  independent  of  those  sources  of  expense 
after  their  first  erection.  This  is  effected  by  the  use  of  heavy 
sheet-iron  housings  for  that  portion  of  the  structure  above  the 
upper  edge  of  the  jacket,  upon  which  fits  a  chimney  of  the 
same  material,  the  iron  in  every  case  being  protected  by  a  4- 
inch  thickness  of  fire-brick,  properly  shaped  to  form  the 
circle. 

Instead  of  the  exterior  crucible  or  fore-hearth  just  described, 
the  Western  water-jackets  are  for  the  most  part  provided 
with  a  cylinder  of  boiler  iron,  which  projects  downward  below 
the  jacket,  forming  an  extension  of  the  same,  and  provided 
with  a  falling  bottom,  consisting  of  two  hinged  iron  doors, 
which,  when  supported  in  place  by  an  iron  bar,  form  a  founda- 
tion for  the  support  of  the  quartz  bottom,  while  the  cylinder 
referred  to  is  lined  with  fire-brick,  thus  forming  an  interior 
crucible,  the  full  size  of  the  furnace,  and  extending  from  16  to 
24  inches  below  the  tuyere  openings. 

In  rare  instances,  the  water-jacket  is  continued  to  the  ex- 
treme bottom  of  the  crucible  ;  but  when  handling  a  product  so 
inclined  to  chill  as  is  metallic  copper,  the  arrangement  just 
described  is  probably  the  best. 

The  peculiarly  favorable  composition  of  the  Copper  Queen 
and  many  other  of  our  Southern  carbonate  ores,  beiag  entirely 
oxidized,  and  containing  an  ample  proportion  of  iron  and  lime, 
has  permitted  the  employment  of  low,  cheap  furnaces,  as  well 
as  the  fusion  of  an  unusual  amount  of  ore  in  proportion  to 
their  size.  And  it  is  to  this  favorable  condition  of  affairs, 
rather  than  to  any  inherent  virtue  on  the  part  of  the  furnaces 
used,  that  the  extraordinarily  long  and  successful  campaigns 
of  the  Copper  Queen  and  neighboring  furnaces  must  be  at- 
tributed.* 

*  As  the  water-jacket  furnace  has  had  its  principal  development  in  the 
smelting  of  oxidized  ores,  and  as  its  whole  construction  and  management  are 
peculiarly  American,  it  seems  proper  to  describe  the  same  with  some  minute- 
ness, taking  as  a  type  the  plant  of  the  Copper  Queen  mine,  of  Arizona,  where, 
under  the  direction  of  Mr.  Lewis  Williams,  it  has  been  thoroughly  adapted 
to  the  surrounding  conditions.  Ample  use  will  be  made  of  the  valuable  paper 
by  Mr.  James  Douglas,  entitled  "  The  Cupola  Smelting  of  Copper  in  Arizona," 
which  was  written  for  the  United  States  Geological  Survey,  Albert  Williams, 
Jr. ,  editor. 


200     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

The  following  figures,  taken  from  Mr.  Douglas's  paper,  are 
average  results  of  regular  work  : 

The  Copper  Queen  smelter  contains  two  36-inch  circular 
wrought-iron  jackets,  each  of  which,  puts  through  from  45  to 
50  tons  of  ore  daily,  flux  being  seldom  required. 

The  very  fusible  ore  of  the  Old  Globe  mine  (Arizona)  is 
smelted  in  a  3-foot  furnace  at  the  rate  of  55  tons  daily,  and 
even  this  extraordinary  result  has  been  exceeded  by  the  United 
Verde  furnace. 

In  nearly  all  cases,  a  No.  4J  or  5  Baker  blower  is  used, 
which,  at  from  100  to  115  revolutions,  supplies  from  5  to  7 
tuyeres  with  wind  at  a  pressure  of  from  10  to  12  ounces. 

The  size  of  the  tuyeres  is  very  variable,  3  inches  being  the 
average  diameter,  although  the  Copper  Queen  management  has 
found  a  decided  advantage,  both  in  capacity  and  in  freedom 
of  the  slag  from  copper,  by  increasing  this  measurement  to  5 
inches. 

About  1,000  fire-bricks  are  required,  on  the  erection  of  the 
furnace,  for  the  lining  of  the  portion  above  the  jacket,  and  for 
the  crucible.  None  is  subsequently  used,  as  the  upper  lining 
lasts  indefinitely,  while  the  crucible  is  kept  from  burning  out 
by  the  introduction  of  siliceous  or  clayey  ore  through  the 
tuyeres,  whenever  a  too  hot  basic  slag  has  thinned  its  walls 
and  bottom  beyond  the  normal  standard.  Any  indications  of 
chilling  up  are  at  once  counteracted  by  a  slight  addition  of 
fuel,  and  by  permitting  the  flame  to  blow  through  the  tap-hole 
and  metal  opening.  *- 

These  orifices,  provided  with  cast  spouts,  are  situated  re- 
spectively 10  and  24  inches  below  the  tuyere  openings,  the  lat- 
ter being  at  the  very  bottom  of  the  crucible. 

They  are  closed  by  inch  bottom-plates,  perforated  with  a 
large  opening,  the  slag  flow  being  cooled  by  water.  Even 
without  such  cooling,  these  plates  are  found  to  possess  decided 
advantages  over  the  ordinary  brick-work  openings. 

The  cooling  water  is  introduced  into  the  jacket  through 
four  l|-inch  pipes,  at  some  distance  above  its  lower  edge,  and 
should  be  deflected  at  right  angles  from  its  horizontal  course, 
experience  having  shown  that  its  constant  spouting  against  the 
hot  inner  iron  plate  causes^  a  rapid  perforation  of  the  same. 


THE   SMELTING   OF   COPPER.  201 

Where  lime  salts  are  present,  it  should  never  be  allowed  to 
reacli  a  high  temperature,  on  account  of  the  formation  of  scale. 

The  small  quantity  of  water  required  after  the  furnace  has 
reached  its  full  burden,  compared  with  what  is  necessary  dur- 
ing the  operations  of  blowing  in  and  out,  although  usually 
attributed  to  the  formation  of  a  coating  of  slag  on  the  interior 
of  the  jacket,  is,  in  the  author's  opinion,  due  rather  to  trans- 
ference of  the  point  of  greatest  heat  to  the  center  of  the  shaft. 
This  arises  from  the  formation  of  slag  noses  around  the  orifices 
of  the  tuyeres,  by  which  the  blast  is  conducted  away  from  the 
walls,  which  are'  thus  left  comparatively  cool. 

The  large  amount  of  water  necessary  to  cool  the  Copper 
Queen  jackets — some  40,000  gallons  daily — suggests  some 
relation  between  that  circumstance  and  the  great  size  of  the 
water-space  in  the  jackets  there  used,  being  9  inches  wide  at 
the  bottom  and  4J  inches  at  the  top.  In  the  Herreshoff  fur- 
nace, and  three  other  jackets  employed  by  the  writer,  the  water- 
space  has  not  exceeded  2  inches,  and  though  the  diameter  of 
the  furnaces  was  considerably  greater  than  that  of  the  Copper 
Queen — all  of  them  being  above  42  inches — a  single  2-inch 
pipe  under  a  slight  head  was  quite  sufficient  to  supply  the 
cooling  water.  This  is  a  point  well  worth  examining,  espe- 
cially where  water  is  scarce  and  costly,  as  in  our  Southern 
carbonate  districts.  It  is  possible  that  the  impure  nature  of 
the  Copper  Queen  water,  requiring  the  removal  through  hand- 
holes  of  the  calcareous  deposit  every  five  weeks,  may  necessi- 
tate the  broad  water-space  used. 

THE   MANAGEMENT  OF  WATER-JACKET  FURNACES. 

The  slight  amount  of  brick-work  in  this  type  of  furnace  re- 
quires but  a  single  night's  drying,  a  brisk  fire  being  maintained 
in  the  crucible,  upon  which  by  four  A.M.  enough  coke  should 
be  thrown  to  fill  the  furnace  some  30  inches  above  the  tuyeres ; 
care  being  taken  to  secure  an  ample  circulation  of  water  through 
the  jacket  before  the  initial  fire  is  kindled. 

By  seven  A.M.  the  coke  should  be  in  full  glow,  the  combus- 
tion at  first  proceeding  slowly,  as  its  sole  air  supply  comes 
from  the  open  tap-hole  and  slag  flow,  but  progressing  very 
rapidly  after  once  attaining  the  tuyere  level.  Instead  of  turn- 


202     MODERN  AMERICAN  METHODS   OP  COPPER  SMELTING. 

ing  on  a  light  blast  at  this  point,  and  gradually  filling  the  fur- 
nace with  alternate  layers  of  charge  and  fuel,  a  much  safer  and 
more  convenient  method  consists  in  filling  the  furnace  level 
with  the  charge-door  before  using  the  blast  at  all,  by  which 
means  all  excessive  heat  is  avoided.* 

A  single  exception  may  be  made  in  favor  of  a  small  inde- 
pendent tuyere,  consisting  of  a  2-inch  pipe  connected  with  the 
blast-pipe  by  a  canvas  hose,  which  should  be  thrust  through 
the  breast  opening  in  an  oblique  downward  direction,  the 
tuyere  orifices  being  tightly  plugged,  so  that  the  flame  may 
issue  from  the  tap-hole — if  such  exist — while  the  whole  in- 
terior of  the  crucible  is  brought  to  a  white  heat.  Fresh  coke 
being  added  until  it  stands  some  30  inches  above  the  tuyeres 
— which  are  left  open — a  charge  of  basic,  easily  fusible  slag 
is  given,  alternating  with  coke  charges  in  the  ratio  of  three 
pounds  of  charge  to  one  of  fuel  for  the  first  three  charges, 
after  which  the  ratio  maybe  changed  to  4  to  1,  while  one-fourth 
of  the  slag  is  replaced  by  the  regular  ore  mixture ;  this  may 
be  continued  for  two  or  three  charges,  when  the  relation  of 
charge  to  fuel  and  of  ore  to  slag  should  be  again  raised,  reach- 
ing under  ordinary  circumstances  a  burden  of  from  5^  to  1  by 
the  time  the  level  of  the  charging-door  is  attained.  Then,  and 
not  before,  a  light  blast  is  turned  on,  and  the  rapidly  sinking 
column  replaced  by  constant  charges  of  ore  and  fuel,  the  pro- 
portions between  the  same  being  regulated  by  the  condition 
of  the  crucible  and  the  appearance  of  the  tuyeres  and  slag. 

It  is  a  matter  of  great  importance  to  make  a  good  start, 
and  especially  where  the  brick  fore-hearth  is  used  to  insure 
a  rapid  current  of  hot,  liquid  slag.  A  delay  of  a  very  few 
moments  while  the  basin  is  first  filling,  or  a  thick,  cold  slag, 
will  cause  the  formation  of  a  chill  that  will  very  probably  fill 
up  the  fore-hearth  to  half  its  extent. 

To  avoid  such  a  mishap,  particular  attention  should  be 
devoted  to  the  selection  of  the  slag  used  for  blowing  in,  and 
no  fear  need  exist  of  its  being  too  basic,  provided  the  latter 

*  The  method  of  blowing-in  here  described,  though  practiced  for  many 
years  by  the  writer,  has  been  lately  recommended  by  a  correspondent  of  the 
Engineering  and  Mining  Journal,  whose  experience  confirms  the  author's 
views. 


THE  SMELTING  OF  COPPEE.  203 

quality  is  due  to  oxide  of  iron  and  not  to  an  excess  of  lime. 
For  this  purpose,  nothing  can  excel  the  so-called  "  metal  slag," 
produced  from  the  fusion  of  roasted  matte,  with  the  addition 
of  just  sufficient  silica  to  produce  a  proper  slag.  While  the 
percentage  of  SiOa  in  this  material  often  falls  below  22  per 
cent.,  no  fear  need  be  entertained  but  what  it  will  become  suf- 
ficiently acid  in  its  passage  through  the  furnace  to  obviate  any 
of  those  troubles  that  arise  from  the  production  of  a  subsili- 
cate  during  ore  smelting.  The  clay  mortar  and  lining  of  the 
crucible  and  fore-hearth,  the  dirt  that  becomes  mixed  with  it 
during  transportation,  and,  above  all,  the  ashes  from  the  fuel, 
will  be  found  quite  sufficient  to  neutralize  any  excess  of  base. 
By  the  gradual  substitution  of  the  ore-charge  for  this  metal 
slag,  a  less  and  less  basic  slag  is  produced,  until  the  normal 
charge  is  reached,  and  the  thin,  blood-red,  smoking,  acrid  slag 
that  first  appears  is  replaced  by  a  white,  steady,  and  slightly 
viscid  stream,  almost  free  from  smoke — unless  unusually  basic 
— and  satisfactory  to  the  experienced  eye.  In  the  water-jacket 
furnace  this  condition  and  the  normal  charge  of  ore  and  fuel 
should  be  reached  within  twelve  hours,  unless  some  drawback 
occurs,  due  to  a  neglect  of  some  of  the  precautions  already 
mentioned,  or  to  a  too  rapid  increase  of  blast  or  of  the  ore 
burden.  Where  sulphide  ores  are  treated,  the  initial  charge 
should  contain  enough  unroasted  ore  to  produce  a  matte 
below  35  per  cent,  copper  for  the  first  two  or  three  tappings. 
By  this  means  the  fore- hearth  is  heated  to  the  proper  point, 
and  the  chilling  due  to  too  rich  a  matte  at  too  low  a  tempera- 
ture is  avoided. 

Where  oxidized  ores  are  treated,  and  an  interior  crucible 
used,  the  means  already  mentioned  will  secure  a  proper  tem- 
perature and  prevent  chilling. 

But  the  exterior  "  steep "  crucible,  although  previously 
heated  to  redness  by  a  coke  fire,  is  pretty  likely  to  become 
partially  filled  by  a  so-called  "  skull,"  or  chill  of  metal,  which 
lines  the  sides  and  bottom  to  the  thickness  of  several  inches, 
rendering  it  impossible  to  tap  and  difficult  to  ladle.  This  chill 
should  be  allowed  to  form  until  the  furnace  has  reached  its 
normal  condition,  and  slag  and  metal  are  flowing  freely,  when 
it  may  be  removed  by  means  of  pointed  bars  and  an  overhead 


204     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

tackle.  It  leaves  a  glowing  hot  crucible,  which,  after  a  little 
repairing,  is  allowed  to  fill  with  the  hot  products,  and  is  then 
carefully  covered  with  a  mixture  of  fine  charcoal  and  ashes,  by 
which  means  it  is  kept  from  chilling  for  a  long  period. 

The  Copper  Queen,  and  nearly  all  water-jacket  furnaces 
running  on  oxidized  ores,  are  provided  with  an  interior  cru- 
cible, in  which  both  slag  and  copper  collect,  the  former  being 
tapped  into  pots  every  six  minutes,  while  the  metal  is  run 
through  the  14-inch  lower  spout  every  half-hour  into  iron 
molds,  mounted  on  wheels,  and  which  hold  about  250  pounds.* 

The  tapping  is  accomplished  with  great  ease,  using  only  a 
light  pointed  iron  rod,  the  aid  of  the  sledge  being  scarcely 
ever  required.  As  the  openings  for  both  slag  and  metal  are 
made  in  jacketed  copper  plates,  they  never  become  too  large 
for  easy  plugging,  and  are  stopped  by  a  minute  ball  of  clay. 

Where  the  ores  are  easily  fusible  and  produce  no  wall 
accretions,  and,  above  all,  where  constant  supervision  and  ex- 
treme care  are  bestowed  upon  the  smelting  process,  as  at  the 
Copper  Queen,  the  length  of  the  campaigns  seems  dependent 
only  upon  the  life  of  the  machinery  and  jacket,  although  it  is 
found  necessary  at  these  works  to  burn  down  the  furnace  to 
the  tuyeres  every  five  weeks  in  order  to  remove  the  calcareous 
sediment  from  the  water-space.  Still,  as  the  crucible  is  not 
cooled  off,  and  as  the  furnace  resumes  its  normal  condition  as 
soon  as  refilled,  these  brief  interruptions  can  scarcely  be  con- 
sidered as  terminations  of  a  campaign. 

The  conditions  at  these  works  are  peculiarly  favorable,  no 
extraneous  flux  being  required  when  proper  proportions  of  ore 
can  be  obtained  from  the  different  levels,  where  calcareous, 
ferruginous,  and  siliceous  mixtures  of  carbonates  and  oxides 
of  copper  are  all  represented.  The  following  analysis  of  the 
average  slag  for  several  months  is  taken  from  the  report  already 
mentioned : 


Per  cent. 


Silica 26-64 

Protoxide  of  iron 42'60 

Manganese 0'30 

Zinc 0-50 

Lime .  9.51 


Per  cent. 

Magnesia 0'20 

Alumina 15*40 

Alkalies  and  loss  ..  ....  4  "85 


100-00 


*  In  almost  every  case  where  Arizona  practice  is  referred  to,  Mr.  J.  Doug- 
las's  paper  has  been  consulted  either  for  direct  information  or  verification. 


THE  SMELTING  OF  COPPER.  205 

The  average  slag  assays  from  the  smelting  of  oxidized  ores 
in  water-jackets  may  be  estimated  at  T75  per  cent,  copper,  con- 
si  sting  of  about  equal  proportions  of  oxidized  and  combined 
copper,  and  of  minute  metallic  globules. 

A  rectangular  water-jacket,  built  for  the  Detroit  S melting- 
Works,  Clifton,  Arizona,  by  Mr.  C.  Henrich,  presents  certain 
interesting  points  for  comparison.  The  cross-section  at  the 
tuyeres  is  33  by  66  inches,  while  10  inches  above  the  same  a 
bosh  is  begun,  so  that  30  inches  above  the  tuyeres  the  cross- 
section  is  enlarged  to  45  by  78  inches.  The  four  lower  cast- 
iron  jackets  terminate  at  this  point,  where  they  are  sur- 
mounted by  four  others,  which  still  diverge  slightly,  so  that 
at  their  upper  surface,  7  feet  6  inches  above  the  tuyeres,  the 
furnace  has  an  inside  section  of  54  by  87  inches,  which  is  re- 
tained to  the  charging-door,  10  feet  6  inches  above  the  tuyeres. 
The  slag-tap  is  6  inches  below  the  latter,  and  the  crucible 
is  14  inches  deep,  lined  with  brick,  and  provided  with  a  drop 
bottom.  There  are  fourteen  2|-inch  tuyeres,  five  on  each  side 
and  two  at  each  end,  receiving  a  blast  of  10  ounces  from  two 
No.  4|  Baker  blowers,  making  115  revolutions.  The  object  of 
the  bosh  is  to  increase  the  reducing  action,  with  the  view  of 
obtaining  cleaner  slags,  a  result  that  is  claimed  to  have  been 
obtained,  the  slags  from  this  furnace  assaying  0'4  per  cent, 
lower  than  from  the  small  perpendicular  furnaces.  There  was 
also  a  saving  in  coke  of  8  per  cent. 

The  ores  smelted  are  mixtures  of  carbonates  and  oxides, 
and,  being  slightly  too  siliceous,  require  the  addition  of  a  small 
proportion  of  limestone  and  iron  to  produce  the  following  slag, 
an  average  of  several  weeks,  as  determined  by  Mr.  S.  James, 
Jr.: 

Per  cent. 

Silica 34-34 

Protoxide  of  iron 32  27 

Manganese 6'24 

Lime 10-13  lOO'OO 

Magnesia 2  '30 

An  elliptical  furnace,  provided  with  sectional  cast-iron 
jackets,  forming  £  bosh  29  inches  high  immediately  above  the 
tuyere  level,  has  been  in  use  for  many  years  for  treating  the 
slags  resulting  from  the  fusion  of  the  Lake  Superior  metallic 
"  mineral  "  in  reverberatory  furnaces,  previous  to  the  refining 


Per  cent. 

Alumina 1 1  "80 

Alkalies  and  loss,  etc 3 '64 


Half  Elevation  Half  Section  E-E 

SLAG  CUPOLA— ELEYATION. 


THE  SMELTING  OF  COPPER. 


207 


operation,  which  is  merely  a  later  stage  of  the  same  fusion.* 
(See  section  on  Refining.) 

The  cupola  referred  to  is  a  modification  of  McKenzie's  pig- 
iron  cupola,  and  has,  in  place  of  distinct  tuyere-openings,  a 
five-eighth  inch  slot  encircling  the  entire  furnace,  and  just 
below  the  water-bosh.  Below  the  tuyeres  is  a  34-inch  deep 
crucible,  nearly  the  full  size  of  the  furnace,  and  closed  by  a 
drop-bottom,  protected  by  a  few  inches  of  sand.  The  water- 
bosh  consists  of  curved  sections  of  cast-iron,  fitted  closely 


Half  Section  A-A. 


Half  Section  B-B, 


SLAG  CUPOLA— PLAN. 


together,  and  five-eighths  of  an  inch  thick  on  the  inner  and 
lower  sides,  while  the  external  and  superior  sides  have  only 
half  an  inch  of  metal.  This  bosh  is  22  inches  high,  and  is 
kept  cool  by  a  three-quarter  inch  supply-pipe,  furnishing  25 
gallons  of  water  a  minute. 

The  cupola  is  7  feet  6  inches  in  height  from  tuyere  level  to 
charging-door,  and  has  a  greater  axis  of  7  feet  and  a. smaller 
one  of  4  feet  9  inches. 

A  peculiar  inverted  siphon  arrangement  for  the  tapping  of 

*The  measurements  and  other  details  of  these  slag  cupolas  may  be  seen 
in  the  accompanying  illustrations,  which  first  appeared  in  connection  with 
Prof.  T.  Egleston's  paper  on  "Copper  Refining  in  the  United  States,"  pub- 
lished in  the  Transactions  of  the  American  Institute  of  Mining  Engineers, 
Vol.  IX.,  of  which  use  is  also  made  in  the  following  descriptions,  as  verify- 
ing the  writer's  own  observations. 


Fig.3 


^^^=^^  <f^ j^-:?-  JS^TC-  ^  ^  ?§^^ 


SLAO  CUPOLA. 


THE  SMELTING  OF  COPPER.  209 

the  blast  during  the  continuous  slag  flow  will  be  noticed  by 
reference  to  the  illustrations.  As  even  during  the  ten-hour 
campaigns  made  by  these  furnaces  (owing  to  the  small  lots  of 
slag  belonging  to  separate  mines),  two  of  these  slag  flows  are 
pretty  thoroughly  used  up,  they  will  hardly  be  likely  to  come 
into  general  use. 

The  material  smelted  is  a  siliceous  slag  from  thereverbera- 
tory  furnaces,  carrjdng  some  15  per  cent,  of  copper  and  over  40 
per  cent,  of  silica.  About  20  tons  are  smelted  in  ten  hours, 
using  anthracite  as  fuel,  brief  attempts  to  use  coke  having  re- 
sulted in  an  increase  in  the  richness  of  the  final  slag.  About  1 
pound  of  coal  is  used  to  smelt  3  pounds  of  slag,  probably  the 
highest  consumption  of  fuel  in  the  United  States.  Blast  is 
furnished  by  a  No.  5^  Baker  blower  at  a  pressure  of  10  ounces 
per  square  inch.  The  metallic  copper  produced  is  impure, 
containing  some  5  per  cent,  of  iron  and  half  of  one  per  cent, 
of  sulphur,  the  latter  coming  from  the  fuel ;  while  the  large 
amount  of  iron  present  is  also  due  to  the  powerful  reducing 
action  of  the  anthracite,  which  seems  necessary  to  decompose 
the  silicate  of  copper  present  in  the  slags.* 

On  account  of  the  daily  blowing  out  of  these  furnaces  for 
the  reasons  already  alluded  to,  and  the  necessity  of  maintain- 
ing a  strict  separation  of  the  material  belonging  to  the  various 
mines,  the  furnace  bottom  and  sides,  up  to  the  water-bosh,  are 
torn  out  and  renewed  every  run.  Although  this  practice  is  made 
necessary  in  order  to  obtain  every  scrap  of  copper-bearing  ma- 
terial belonging  to  each  special  campaign,  still  the  deeply  eaten 
and  worn  condition  of  the  brick  lining  shows  that  metallurgical 
reasons  also  exist  for  this  laborious  and  expensive  custom. 

In  common  with  the  Arizona  furnace  managers,  those  at 
Houghton  (Lake  Superior)  have  also  found  that  the  slag  flow- 
ing from  the  furnace  contains  an  appreciable  amount  of  copper 
in  the  shape  of  fine  beads,  technically  denominated  "  prills." 
In  both  localities,  recourse  has  been  had  to  an  independent 
fore-hearth,  consisting  of  a  rectangular  iron  box,  in  which  the 
metal  settles  during  the  slow  progress  of  the  slag. 

*The  formation  of  so  large  an  amount  of  silicate  of  copper  daring  the 
primary  smelting  in  reverberatories  might  possibly  be  prevented  by  the  ad- 
dition of  fine  coal  to  the  charge,  although,  of  course,  its  fusibility  would  be 
somewhat  lessened  thereby. 
14 


210     MODEEN  AMERICAN  METHODS   OF  COPPER   SMELTING. 


This  fore-hearth  at  Lake  Superior  is  lined  with  a  mixture 
of  clay  and  sand,  and  is  6  feet  6  inches  long,  3  feet  6  inches 
wide  at  the  middle,  and  2  feet  9  inches  at  each  end,  being 
slightly  oval  in  shape.  A  considerable  quantity  of  scrap-iron 
is  placed  in  it  at  the  beginning  of  the  run,  with  the  view  of  re- 
ducing to  metal  the  oxidized  copper  contents  of  the  slag,  and 
is  successful  to  the  extent  of  saving  some  10  per  cent,  more  than 
when  omitted.  A  cake  of  from  150  to  200  pounds  is  usually 
obtained  from  the  daily  run,  from  a  charge  of  20  tons  of  slag, 
yielding  15  per  cent,  of  copper,  the  fore-hearth  therefore  sav- 
ing about  2 J  per  cent,  of  the  entire  metallic  contents.  The  slag 
from  these  cupolas  is  very  clean,  considering  the  grade  of  the 
product,  and  is  reported  to  average  below  O75  per  cent.,  rarely 
reaching  one  per  cent.  It  is  rejected  as  worthless. 

The  fore-hearth  in  use  at  the  Copper  Queen  furnaces  for 
catching  the  entangled  metallic  shot  is  a  rectangular  box,  made 
of  four  cast  plates  and  mounted  on  small  wheels.  Its  inside 
dimensions*  are  4  by  2J  feet,  and  30  inches  deep.  It  is  lined 
with  a  mortar  of  clayey  ore,  and  in  an  average  life  of  36  hours 
yields  about  150  pounds  of  copper,  besides  the  metal  entangled 
in  the  chilled  slag  with  which  it  becomes  filled.* 

The  following  table,  compiled  from  the  articles  already  ac- 
knowledged and  from  the  writer's  own  notes,  exhibits  com- 
paratively certain  points  of  interest  pertaining  to  the  smelting 
of  oxidized  ores  in  water-jacketed  cupolas : 


g£ 

| 

1 

1.2 

2 
g-3 
®«2 

2o5 
tUD 

ll 

I 

1 

NAME  op  SMELTING  COMPANY. 

£.2 

<M 

<3 

*o  ^ 

V.»H 

g 

-1 

! 

&  n 

•^  G- 

1! 

ll 

ll 

S° 

C) 

•cl 
c  S 

g-5 

B 

K 

£" 

i£0 

fSft 

£* 

r 

1" 

Detroit      Refining      Works 

Continuous 

(Hough  ton,  Mich.)  

24f 

7 
7 

tuyere. 
6 

Q 

134 
75 
64 

10 

10 
10 

3  00 
5-90 

*i 

5-90 

40-00 

47  00 

56  00 
47-00 

Copper  Queen  

Old  Dominion  

Detroit  C'r  Co.,  large  furnace 

11-8 

14 

83 

12 

6-55 

7-02 

79-15 

86-65 

small       " 

7 

6 

58 

10 

5-55 

rt-oo 

45-00 

48-60 

Arizona  C'r  Co.,  large  furnace 

12-5 

6 

64 

10 

7-75 

75-00 

small      " 

7 

6 

58 

10 

7-75 

55.00 

United  Verde  

7 

6 

58 

10 

.... 

5-00 

52-00 

*  See  section  on  Brick  Cupolas  for  other  varieties  of  fore-hearth. 


THE   SMELTING  OF  COPPER.  211 

A  noteworthy  feature  of  the  Arizona  cupola  practice  is  the 
purity  of  the  product,  averaging  between  97-  and  98  per  cent, 
of  metallic  copper.  Its  freedom  from  injurious  substances  is, 
of  course,  due  to  the  quality  of  the  ore ;  but  the  low  percent- 
age in  iron  of  pig-copper,  produced  in  many  instances  from 
highly  ferruginous  ores,  and  by  a  process  of  reduction  so 
powerful  that  only  traces  of  oxidized  copper  remain  in  the  slag, 
must  be  attributed  to  the  rapidity  of  the  fusion.  This  in  its 
turn  results  principally  from  the  volume  and  pressure  of  the 
blast  and  suitability  of  the  fuel,  which  consists  in  most  cases 
of  a  coke  of  tolerably  good  quality  from  Trinidad,  Colorado^ 
or  San  Pedro,  New  Mexico,  the  latter  containing  less  ash,  but 
being  of  a  more  friable  nature.  With  Connellsville  (Pennsyl- 
vania) coke,  a  slightly  higher  ratio  of  ore  to  fuel  is  obtained,, 
and  a  patent  Cardiff  coke  gives  the  best  results  of  all.  The 
average  contents  of  ash  in  the  Trinidad,  San  Pedro,  and  Con- 
nellsville cokes  is  reported  respectively  at  14- 6,  13*2,  and  11*6 
per  cent.  Sufficient  sulphur  is  present  in  nearly  all  the  Ari- 
zona carbonate  ores  to  form  a  small  proportion  of  matte,  which 
in  many  cases  is  simply  thrown  back  into  the  furnace  without 
further  treatment,  while  other  companies  more  sensibly  sack 
and  ship  it  East  as  a  separate  product.  It  varies  between  a 
high-blue  metal  and  a  low- white  metal  from  60  to  66  per  cent, 
and  could  be  advantageously  roasted  twice  in  heaps  and  mixed 
with  the  ore-charge  in  small  quantities. 

At  the  Copper  Queen  Works,  a  kiln  is  used  for  the  roasting 
of  whatever  matte  may  be  produced,  though  its  occurrence 
is  very  irregular.  Sometimes  for  several  successive  days,  as 
much  as  1,500  pounds  per  day  will  be  made,  and  is  easily  sepa- 
rated from  the  bars  of  metal  on  which  it  floats.  At  other  times 
for  months  together,  not  a  trace  of  matte  will  occur  ;  nor  does 
the  depth  from  which  the  ore  is  mined  have  any  influence  on 
its  production,  for  the  sulphide  ores  which  cause  it  are  found 
full  as  abundantly  in  the  upper  as  in  the  lower  levels. 

Even  the  freedom  from  all  concentration  and  calcination 
processes  does  not  entirely  relieve  the  Arizona  smelters  from 
that  great  curse  of  blast-furnace  work — the  occurrence  of  a 
considerable  proportion  of  fine  ore.  The  clayey  and  friable 
nature  of  many  of  the  ferruginous  and  calcareous  carbonates 


212     MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

favors  the  formations  of  fines,  which,  aside  from  the  heavy  loss 
entailed  by  their  escape  through  the  stack,  clog  the  furnace, 
obstruct  the  blast,  and,  being  sifted  down  between  the  coarser 
lumps  of  ore  and  fuel,  reach  the  smelting  zone  in  a  cold  and  un- 
prepared condition,  causing  the  chilling  of  the  crucible  and  the 
growth  of  long  noses  from  each  tuyere,  which  may  meet  in  the 
middle,  forming  a  central  core  of  semi-fused  material  that  may 
necessitate  the  termination  of  the  campaign.  The  loss  in  flue- 
dust  is  partially  remedied  at  the  Copper  Queen  and  one  or 
two  other  furnaces  by  the  construction  of  flues  and  dust-cham- 
bers. The  clayey  nature  of  most  of  the  fines,  and  the  hot  and 
dry  climate,  assist  the  process  of  bricking  these  fines,  although 
in  certain  cases  an  addition  of  milk  of  lime  is  found  necessary 
to  bind  the  particles  together  with  sufficient  firmness. 

Most  of  the  ores  being  of  a  basic  and  decomposed  nature, 
a  very  small  amount  of  mechanical  preparation  for  the  fur- 
nace is  demanded.  At  most  works,  the  ore  is  merely  passed 
through  a  jaw-breaker,  set  to  a  size  of  from  2  to  3  inches. 

For  th  reasons  already  enumerated,  a  height  of  the  fur- 
nace from  tuyere  to  charging-door  of  more  than  seven  feet  is 
rarely  met  with  in  this  particular  practice. 

The  use  of  round  or  oval  furnaces  of  the  water-jacket  type 
has  become  almost  universal  in  copper  smelting,  probably 
owing  to  their  ease  of  construction.  A  long  and  varied  trial 
by  the  writer  of  almost  every  style  and  size  of  cupola  was  so 
indubitably  in  favor  of  the  rectangular  or  elongated  oval  form, 
and  more  especially  of  very  much  larger  furnaces  than  any  yet 
described,  both  for  economical  reasons  and  for  ease  and  sim- 
plicity of  management,  that  the  comparative  want  of  success 
in  certain  reported  cases  is  apparently  attributable  to  other 
causes  than  a  mere  incapacity  on  the  part  of  the  furnace  to 
fulfill  all  expectations  based  on  comparative  calculations.  The 
new  furnace  built  by  the  Detroit  Smelting  Company,  of  Michi- 
gan, which  is  much  larger  than  the  older  ones,  is  entirely  satis- 
factory, and  works  with  increased  economy,  reaching  a  result 
fully  equal  to  its  theoretical  capacity. 

The  great  size  of  the  furnaces  preferred  by  the  writer  has, 
until  quite  recently,  prevented  the  employment  of  water- 
jackets,  so  that  their  description  and  discussion  must  be  de- 


THE  SMELTING  OF  COPPER.  213 

ferred  to  the  section  on  Brick  Blast-Furnaces,  but  since  the 
success  of  quite  large,  oval,  wrought-iron  jacketed  cupolas  has 
been  assured,  there  can  be  but  rare  instances  where  brick  fur- 
naces would  be  preferred. 

The  life  of  a  water-jacket  in. constant  use  depends  so  en- 
tirely upon  its  treatment  and  upon  the  quality  of  the  feed-water 
that  it  is  impossible  to  fix  any  exact  limit  for  it.  Cast-iron 
jackets  may  last  from  one  to  four  years,  though  sometimes 
cracking  in  a  few  days,  while  wrought  shells  have  been  run 
almost  constantly  for  six  years  without  any  considerable  re- 
pairs. Under  the  most  favorable  conditions,  and  in  the  lack 
of  more  extended  experience,  five  years  may  be  assumed  as  the 
duration  of  a  wrought-iron  jacket  in  constant  use. 

Estimates  of  cost  would  be  superfluous,  the  manufacturer's 
price-lists  and  cost  of  boiler  work  and  piping  supplying  all 
needful  bases  for  calculation. 

Owing  to  the  comparatively  recent  introduction  of  water- 
jacketed  furnaces  with  improved  arrangements  for  crucible  and 
fire-hearth,  there  is  a  great  lack  of  accurate  information  on 
the  subject,  and  any  reliable  details  of  their  performance, 
capacity  under  differing  conditions  of  blast  and  charge,  etc., 
etc.,  are  valuable.  On  this  account,  the  table  given  below, 
compiled  from  the  records  of  practice,  although  not  as  full  or 
complete  as  desirable,  will  still  be  found  of  value. 


214     MODERN  AMERICAN  METHODS  OF   COPPER  SMELTING. 


•no 


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B0BIV  U-     -     -< 


COTS 


position 
roduct. 


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oo      osoo 


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ut 


jo 


UI     89J9AUJ 
JO    B9J 


jo 


•pnj 

jo   'juao  jaj  |  $2 


Connells 
Gas-cok 


J9d    saouno 
jo 


Grave 

Metal  slag 
Siliceous 
bonat 


1  •  «  i  : 
5|  Bit 

'El  lh 

S^3     ^J=  O 
O          S       S 


: »     ,   1  •  'I  :  § 


ite 
carb 

matt 
tte 


11  !l    llill.1 


ne 
er 
s 
ne 


ce 
es 


™l!i|Iti 

O    O        O     0^ 


Cal 
Wes 
at 
Cal 


"i-iKj   cft^r  uacc 

tuitft. 


(Barf    aCettwefc'* 

3 11 1  p  i  o  ue  i  n  c  ti  L> 

for 

Copper  0re&. 


BARTLETT    WATER-JACKET — WATER-TANK   ARRANGEMENT. 


CHAPTEE  X. 

BLAST-FURNACES  CONSTRUCTED  OF    BRICK. 

THE  small  type  of  brick  cupolas,  though  not  yet  entirely 
abandoned  in  the  United  States,  in  the  treatment  of  copper 
ores  and  mattes,  has  been  described  in  almost  every  former 
work  on  this  subject,  and  it  possesses  no  peculiar  or  distinct- 
ive features  that  demand  particular  attention. 

As  the  whole  tendency  of  the  art  looks  toward  an  increase 
in  the  size  and  capacity  of  most  of  our  metallurgical  structures, 
particular  attention  is  here  given  to  such  details  as  are  not  to 
be  found  elsewhere  in  metallurgical  literature. 

The  largest  type  of  brick  cupola  as  yet  found  unmistakably 
practicable  and  advantageous  will,  therefore,  be  selected  for 
detailed  description,  the  accumulated  experience  of  several 
years,  and  covering  almost  every  grade  and  variety  of  copper- 
bearing  material,  having  emphatically  demonstrated  its  econ- 
omy and  general  superiority. 

That  the  bounds  of  economy  have  not  been  overstepped  in 
this  matter  of  size  is  evident  from  careful  comparative  experi- 
ments, which  show  conclusively  that  the  cost  per  ton  of  ore  in- 
creases, the  repairs  become  proportionately  greater,  and  the 
ease  of  management  is  sacrificed  with  every  inch  that  is  taken 
from  the  size  already  referred  to.  What  the  limits  may  be  in 
the  other  direction  is  yet  an  open  question ;  but  experience 
has  shown  that  any  further  considerable  augmentation  of  ca- 
pacity involves  the  solution  of  various  new  problems  pertain- 
ing to  the  blast  and  to  the  handling  of  such  large  quantities  of 
ore  and  slag,  and  certain  other  matters  that  will  be  noticed  in 
their  proper  place.  It  would  be  unjust  to  attempt  the  history 
or  description  of  the  successful  introduction  of  this  form  of 
large  rectangular  brick  furnaces  without  mentioning  the  names 
of  certain  persons  whose  perseverance  and  skill  have  overcome 
the  difficulties  inseparable  from  such  an  undertaking,  and  who 


\ 
216      MODERN  AMEEICAJST  METHODS   OF  COPPER  SMELTING. 

have  made  to  American  metallurgy  one  of  its  most  valuable 
additions.* 

The  distinctive  peculiarities  of  the  "  Orford  "furnace,  as 
this  altered  and  improved  form  of  Kaschette  furnace  is  usually 
designated,  aside  from  its  unusual  size,  are  the  large  number 
and  diameter  of  its  tuyere  openings — 14  of  6  inches  diameter  ; 
the  absence  of  any  interior  crucible  or  space  for  the  collection 
of  the  fused  products ;  the  substitution  therefor  of  an  exte- 
rior fore-hearth  or  basin,  and  the  construction  of  the  latter  in 
such  a  manner  that  two  continuous  streams — of  slag  and  metal 
respectively — flow  therefrom  into  ordinary  slag-pots,  without 
any  blowing  through  of  the  blast,  or  delay  for  tapping  and 
other  related  manipulations.  The  latter  arrangement  may  be 
applied  to  any  furnace  of  sufficient  size,  it  being  absolutely  es- 
sential, for  the  prevention  of  chilling,  that  a  large  quantity  of 
molten  material  should  constantly  traverse  it.  If  the  product 
is  a  matte  of  high  grade,  60  per  cent,  and  over,  a  much  larger 
quantity  is  necessary  to  prevent  chilling  than  if  the  metal  is  of 
poorer  quality.  The  rapid  chilling  of  the  former  is  due  not  to 
its  possessing  a  higher  fusion  point,  but  because  its  capacity 
as  a  conductor  of  heat  increases  with  its  percentage  of  copper. 

When  the  smelting  mixture  is  exceedingly  rich,  so  that  a 
very  large  amount  of  the  copper-bearing  product  results,  it  is 
even  possible,  by  rapid  smelting,  to  maintain  a  constant  stream 


*  The  gentlemen  referred  to,  Messrs.  W.  E.  C.  Eustis,  R.  M.  Thompson, 
H.  M.  Howe,  J.  L.  Thomson,  are,  or  have  been,  all  officers  of  the  present 
Orford  Copper  and  Sulphur  Company,  of  Bergeuport,  New  Jersey  ;  and  while 
the  furnace  referred  to  closely  resembles  the  Raschette  type  of  furnace  so  exten- 
sively introduced  into  Germany  and  Russia  during  the  past  thirty  years,  its 
management  and  all  manipulations  connected  therewith  are  sufficiently  dif- 
ferent to  convert  into  a  brilliant  success  what  has  in  Europe,  at  least,  been 
practically  a  failure.  The  application  of  the  exterior  crucible,  continuous 
matte-tap,  and  peculiar  method  of  feeding  and  manipulation  by  which  cam- 
paigns of  a  year  are  made  with  an  excessively  basic  slag,  and  in  the  entire 
absence  of  any  water-cooled  tuyeres,  aside  from  the  trebling  of  its  former 
capacity,  are  sufficient  to  constitute  a  valid  claim  to  originality. 

The  writer  is  pleased  to  have  this  opportunity  to  acknowledge  the  benefits 
derived  from  long  and  intimate  intercourse  with  these  gentlemen,  and  to 
state  that  it  was  while  occupying  the  position  of  superintendent  of  this  com- 
pany that  he  first  learned  the  full  extent  to  which  the  cost  of  smelting  could 
be  reduced  by  increase  in  the  capacity  of  furnaces. 


BLAST-FURNACES   CONSTRUCTED  OF  BRICK. 


217 


of  metallic  copper — a  practice  that  may  be  regarded  as  a  curi- 
osity rather  than  as  ordinarily  feasible. 

A  detailed  description  of  the  construction  and  subsequent 
management  of  this  form  of  furnace  will  bring  forward  the 


ORFORD  BRICK  FURNACE. 


points  already  referred  to,  and  illustrate  the  practice  that  up 
to  the  present  time  has  been  found  most  advantageous,  and 
which  has  cheapened  the  smelting  of  copper  ores  to  a  remark- 
able extent. 

The  outside  measurement  of  the  furnace  being  8  feet  5 


218      MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

inches  by  16  feet  8  inches,  an  excavation  should  be  made  at 
the  intended  site  some  three  feet  larger  in  every  direction  than 
the  figures  just  given,  and  of  sufficient  depth  to  reach  solid 
ground  and  insure  a  proper  foundation.  A  depth  of  4  or 
5  feet  will  usually  suffice,  the  pit  being  immediately  filled 
with  concrete ;  or,  where  possible,  the  pit  should  be  filled  to 
nearly  the  surface  with  molten  slag. 

The  walls  of  the  furnace  should  be  begun  a  foot  below  the 
ground  level,  and  should  consist  entirely  of  fire-brick  up  to  the 
tuyere  level,  where  the  panels,  shown  in  the  cut,  are  begun. 
Up  to  this  point,  the  walls  are  30  inches  thick,  of  solid  fire- 
brick, while  the  panels  are  only  18  inches  thick,  thus  being 
more  accessible  for  repairs,  and  containing  the  tuyere  open- 
ings. The  rear  wall  is  divided  into  three  panels,  equally 
spaced,  and  supported  on  each  side  by  the  full  thickness  of 
the  wall,  forming  columns  at  each  corner,  and  between  the 
weaker  portions,  that  are  chiefly  relied  upon  to  carry  the 
weight  of  the  superincumbent  structure.  The  panels  are  30 
inches  wide  and  33  inches  high,  and  are  strongly  arched  over 
with  three  rows  of  fire-brick,  above  which  the  full  thickness  of 
the  wall  (30  inches)  is  maintained  to  the  top  of  the  structure. 
Each  panel  is  pierced  by  two  6-inch  square  tuyere-holes, 
equally  spaced,  excepting  the  central  front  panel,  which  con- 
tains only  a  small  orifice  for  the  slag-run,  at  a  point  some  10 
inches  below  the  tuyere  level.  The  panel  referred  to  forms 
the  breast  of  the  furnace,  and  is  not  closed  in  until  the  last 
moment. 

The  total  number  of  tuyere  openings  is  14 — 6  behind,  4  in 
front,  and  2  at  each  end.  The  interior  rectangle  is  3  feet  5 
inches  wide  and  11  feet  8  inches  long,  although  any  exact  ad- 
herence to  these  measurements  is  unnecessary,  the  interior  of 
the  furnace  being  soon  burnt  out  into  an  irregular  shape  and 
usually  much  larger  than  the  size  just  given. 

Strong  tie-rods,  provided  at  their  extremities  with  loops,  and 
buried  deeply  in  the  foundation,  are  placed  in  position  as  indi- 
cated in  the  cut.  Unless  the  transverse  rods  can  be  placed  at 
a  depth  of  two  or  three  feet  below  the  surface,  they  should 
merely  be  fastened  into  the  wall  by  hooks,  as  they  would  cer- 
tainly be  smelted  away  in  time. 


BLAST-FURNACES   CONSTRUCTED   OF  BRICK. 


219 


.,!•.„„ 


SIDE  VIEW. 


6'S 


FRONT  VIEW. 


SCALE  ft  /N.  TO  THE  FOOT 

THE  ORPOKD  "BASCHBTTE1'  FUKXACE. 


220     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 


The  brick  should  be  laid  with  the  closest  possible  joints, 
and  in  a  very  thin  mortar  made  of  half  each  of  raw  and  burned 
fire-clay,  ground  exceedingly  fine. 

Heavy  railroad  iron  may  be  used  for  binders,  and  should  be 
used  rather  more  than  less  liberally  than  shown  in  the  illus- 
tration, as  the  expansive  force  is  enormous  when  the  furnace  is 
in  full  heat,  and  any  serious  cracking  tends  greatly  to  shorten 
its  existence. 

If  fire-brick  are  expensive,  the  outside  lining,  above  the 


SECTION  A  B. 


SECTION  CD.  SECTION  G M, 

THE  ORFORD  "  RASCHETTE  "  FURNACE. 

panels,  and  to  a  depth  of  12  inches,  may  be  constructed  of  red 
brick,  although  this  is  not  recommended. 

The  usual  height  from  the  tuyeres  to  the  threshold  of  the 
charging-door  is  8  feet ;  but  this,  of  course,  may  be  varied  to 
suit  the  character  of  the  ore  to  be  smelted.  The  charging- 
doors  are  three  in  number,  and  of  large  size.  All  further  de- 
tails of  construction  are  plainly  shown  in  the  cut. 

The  chimney  should  never  be  made  smaller  than  here 
shown,  and  if  a  vertical  down-take  is  used,  connected  with  flues 
for  the  saving  of  the  flue-dust,  its  dimensions  should  be  in- 
creased one- third.  The  latter  construction  is  much  preferable 


BLAST-FURNACES  CONSTRUCTED  OF  BRICK.  221 

to  the  simple  vertical  chimney,  and  is  absolutely  essential  where 
anything  but  the  poorest  material  is  smelted,  as  the  loss  in 
flue-dust,  owing  to  the  enormous  volume  of  blast  peculiar  to 
this  practice,  is  very  great — especially  as  a  large  proportion  of 
the  charge  often  consists  of  fine  ore,  it  having  been  found  that 
these  large  rectangular  furnaces  are  peculiarly  adapted  to  the 
treatment  of  that  material. 

The  tuyeres  consist  of  rather  heavy  galvanized  sheet-iron 
— No.  18 — and  are  connected  with  the  vertical  branches  of  the 
main  blast-pipe  surrounding  the  furnace  with  thick  duck  tuyere- 
bags,  soaked  in  a  strong  solution  of  alum,  to  render  them  less 
inflammable  and  to  fill  the  pores  of  the  cloth.  Their  diameter 
may  vary  with  the  character  of  the  ore  under  treatment,  but  is 
usually  from  five  to  six  inches,  the  pipes  being  merely  thrust 
a  short  distance  into  the  square  orifices  left  in  the  brick-work, 
and  made  tight  with  plastic  clay. 

There  remains  nothing  in  the  construction  of  this  furnace 
that  cannot  be  plainly  seen  from  the  illustration,  and  the  dis- 
cussion of  its  management  from  the  time  when  taken  in  hand 
by  the  smelter  will  now  be  proceeded  with. 

It  is  frequently  customary  to  form  the  bottom  of  a  solid 
mass  of  fire-brick,  placed  on  end,  and  brought  up  to  within  10 
inches  of  the  tuyere  openings,  sloping  slightly  toward  the  slag- 
run  in  the  center  of  the  front  wall.* 

The  author  has  found  the  following  method,  practiced  orig- 
inally by  the  Orford  Company,  far  superior  to  any  other,  espe- 
cially where  low-grade  matte  is  to  be  produced,  the  most 
difficult  of  all  copper-bearing  materials  to  confine  within  brick 
walls. 

After  filling  in  the  foundation  with  beton  to  a  foot  below 
the  ground  level,  the  furnace  bottom  is  begun  by  laying  two 
courses  of  fire-brick  on  end,  and  with  the  closest  possible  joints. 
This  still  leaves  a  space  of  from  24  inches  to  30  inches  to  bring 
the  bottom  to  the  proper  height,  which  is  filled  in  as  follows  : 

The  furnace  and  foundation  being  thoroughly  dried  by  at 

*  The  practice  of  basing  the  bottom  upon  an  arch  built  over  an  open  space 
below  must  be  strongly  condemned,  as  it  will  simply  result  in  the  cutting 
through  of  the  arch,  and  the  total  disappearance  of  all  metal  until  the  cavity 
is  filled,  making  eventually  a  solid  but  somewhat  expensive  bottom. 


222     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

least  four  days'  brisk  firing  with  brands  and  similar  material, 
enough  coke  is  dumped  into  the  red-hot  shaft  to  fill  it  to  a 
point  some  three  feet  above  certain  temporary  openings  that 
should  be  left  in  the  brick-work  while  building.  These  openings 
correspond  in  size,  number,  and  position  with  the  permanent 
tuyere  openings,  except  that  they  are  some  8  inches  lower  and 
directly  beneath  the  regular  orifices,  which,  for  the  present, 
are  plugged  with  clay. 

Some  six  or  eight  tons  of  calcined  quartz  crushed  to  the 
size  of  chestnuts  and  mixed  with  about  5  per  cent,  of  fusible 
slag,  are  spread  upon  the  coke  ;  and  as  soon  as  the  latter  is 
properly  on  fire  above  the  temporary  tuyere  openings,  the 
blast-pipes  are  put  in  place,  and  a  light  blast  is  continued  until 
the  coke  is  burned  away,  and  the  sticky,  half-melted  charge 
threatens  to  flow  into  the  tuyere  openings.  The  unconsumed 
coke  and  excess  of  quartz  are  removed  through  the  breast 
panel — which  was  built  up  temporarily  of  4-inch  brick-work  ; 
and  the  furnace,  being  tightly  closed,  is  allowed  to  cool  very 
gradually  for  twenty-four  hours  or  more. 

If  the  operation  is  successful,  the  bottom  will  be  as  solid 
and  infusible  as  can  be  made,  nor  will  any  attempt  at  the  sub- 
stitution of  basic  material  for  quartz,  in  consideration  of  the 
probable  highly  ferruginous  character  of  the  slag  to  be  pro- 
duced, result  in  any  improvement  on  the  plan  recommended. 

It  is  probably  as  good  a  bottom  as  can  be  made,  although, 
as  will  be  later  seen,  it  offers  but  little  resistance  to  a  hot  low- 
grade  matte,  when  produced  at  the  rate  of  from  30  to  50  tons 
daily. 

The  furnace  being  thoroughly  dried  and  heated,  blowing  in 
may  follow  at  once,  it  being  only  necessary  to  plug  the  tem- 
porary tuyere  orifices,  fill  the  shaft  with  coke  to  a  point  some 
3  feet  above  the  permanent  tuyeres,  and  allow  the  fire  to  ascend 
to  these  openings  before  filling  the  shaft  with  alternate  layers 
of  charge  and  fuel,  and  putting  on  a  light  blast  (one  ounce). 
All  this  may  be  done  the  night  before  starting,  and  at  the 
same  time,  if  not  before,  the  fore-hearth  and  siphon-tap  *  must 

*  This  is  an  entire  misnomer,  as  the  apparatus  here  referred  to,  as  used 
for  the  continuous  discharge  of  the  metallic  product,  has  nothing  about  it 
pertaining  to  the  principles  of  the  siphon. 


BLAST-FURNACES   CONSTRUCTED  OF  BRICK.  223 

be  arranged.  This  consists  of  a  rectangular  box,  some  4  feet 
by  3  feet  6  inches,  formed  of  cast-iron  plates  strongly  bolted 
together  at  the  corners,  and  lined  with  a  brick  wall  4J  inches 
or  9  inches  thick,  according  to  the  quality  of  the  product.  It 
is  fastened  firmly  to  the  front  of  the  furnace,  just  at  the  slag- 
run  in  the  center  panel,  the  lower  middle  portion  of  the  ante- 
rior front  wall  of  that  structure  forming  its  posterior  boundary. 
It  is  divided  longitudinally  by  a  9-inch  wall  of  fire-brick  into 
a  greater  and  lesser  portion,  the  area  of  the  two  compartments 
being  about  as  5  to  2,  and  the  direction  of  the  division  wall 
being  parallel  to  the  short  axis  of  the  furnace. 

The  entire  molten  contents  of  the  furnace  discharge  through 
a  2  by  4-inch  opening  (the  slag-run)  in  the  middle  panel  (the 
breast)  into  the  larger  of  these  two  compartments,  which  is 
provided  with  a  slag-spout,  bolted  to  the  upper  edge  of  the 
front  plate,  while  it  communicates  with  the  smaller  compart- 
ment by  means  of  a  3-inch  by  8-inch  vertical  slot  through  the 
9-inch  division  wall,  about  midway  of  its  length  and  on  a  level 
with  the  floor  of  the  fore-hearth.  This  smaller  compartment 
also  has  a  spout  about  2  inches  below  the  level  of  the  spout 
belonging  to  the  larger  division,  and  on  the  outer  side — in- 
stead of  the  end  wall,  for  the  sake  of  convenience. 

A  thorough  understanding  of  this  very  simple  and  inexpen- 
sive contrivance  will  render  it  very  easy  to  appreciate  its  man- 
agement. 

When  the  breast-hole  is  opened,  and  slag  and  metal  first 
begin  to  flow,  the  larger  compartment  is  soon  filled,  as  the  only 
means  of  communication  between  the  two  divisions  of  the  fore- 
hearth  is  the  closed  slot  in  the  lower  part  of  the  9-inch  divi- 
sion wall. 

The  molten  products  separate  according  to  the  law  of  gravity, 
and  slag  is  allowed  to  flow  through  the  spout  of  the  large  com- 
partment until  the  drops  of  metal  appearing  show  that  it  is  filled 
with  the  more  valuable  product.  The  channel  of  communica- 
tion is  now  opened  by  means  of  a  crooked  tapping-bar,  and 
the  metal  flows  rapidly  through  the  same  into  the  smaller  com- 
partment, until  an  equilibrium  is  established,  and  both  divi- 
sions of  the  fore-hearth  are  partially  filled  with  the  matte,  the 
communicating  channel  being  far  below  the  surface  of  the  same, 


224     MODERN  AMERICAN  METHODS  OF  COPPER  SMELTING. 

and  consequently  so  situated  that  slag  can  never  reach  it  un- 
less it  should  sink  below  the  metal,  which  is  obviously  im- 
possible. 

As  the  furnace  constantly  discharges  its  stream  into  the 
larger  compartment,  the  fore-hearth  is  soon  filled  again,  the 
metal  sinking  to  the  bottom  and  standing  at  the  same  level 
in  both  divisions,  while  the  slag  simply  flows  over  the  surface 
of  the  matte  in  the  larger  compartment. 

As  soon  as  the  matte  reaches  the  level  of  the  spout  attached 
to  the  small  compartment,  it  begins  to  flow  into  a  pot  placed 
to  receive  it,  and  by  judicious  manipulation,  and  if  a  sufficient 
proportion  of  matte  is  produced  from  the  charge,  a  constant 
stream  of  each  product  maybe  kept  running  without  difficulty. 

The  management  of  this  "  siphon-tap  "  requires  consider- 
able experience,  as  the  matte  stops  occasionally  without  ap- 
parent cause,  and  requires  a  certain  amount  of  manipulation 
and  coaxing  to  keep  running  freely.  This  is  accomplished  by 
slightly  damming  up  the  slag-spout,  which  soon  forces  an  ex- 
cess of  matte  into  the  smaller  compartment,  or  by  clearing  out 
the  communicating  orifice  by  means  of  a  heated  bar  bent  to 
the  required  curve. 

With  matte  of  50  per  cent,  or  over,  the  principal  difficulty 
is  found  in  the  gradual  filling  up  of  the  fore-hearth  by  chilling, 
while  a  matte  containing  20  per  cent,  or  less  of  copper,  and 
produced  in  large  quantities,  has  directly  the  opposite  effects, 
thinning  the  fire-lining  until  the  plates  are  endangered,  and 
cutting  away  the  division  wall  until  the  two  compartments  are 
virtually  thrown  into  one. 

But  even  under  these  circumstances,  and  as  long  as  a  ves- 
tige of  the  center  wall  remains,  the  separation  of  the  matte  and 
slag  continues  to  be  perfect,  and  by  judicious  repairing  and 
nursing,  a  fore-hearth  apparently  in  the  last  stage  of  ruin  may 
yet  do  good  service  for  many  days. 

An  opening  through  the  division  wall  18  inches  high  by  24 
inches  wide,  and  actually  involving  two  thirds  of  the  separat- 
ing brick-work,  is  not  incompatible  with  a  perfect  separation. 

The  larger  compartment  is  provided  with  a  tap-hole  at  its 
lowest  boundary,  and  on  the  side  opposite  the  matte  division, 
and  a  large  quantity  of  sand  should  always  be  at  hand  ready 


BLAST-FUENACES  CONSTEUCTED  OF  BEICK.  225 

to  make  up  into  rough  molds  in  case  of  any  sudden  necessity 
for  tapping  the  furnace. 

This  is  especially  the  case  when  producing  very  low-grade 
metal ;  for  owing  to  its  corrosive  action,  and  to  the  fact  that 
the  anterior  wall  of  the  furnace  forms  the  posterior  boundary 
of  the  fore-hearth,  the  entire  contents  of  the  former  may  escape 
into  the  latter  in  case  of  a  break  through  the  plates.  It  is  at 
first  somewhat  startling  to  have  such  an  outbreak  when  the 
entire  bottom  of  the  enlarged  and  burned-out  furnace  has  been 
excavated  to  the  floor  level,  forming  a  crucible  some  three 
feet  deep  and  perhaps  4  by  13  feet  in  size.  Under  such  cir- 
cumstances, the  emptying  of  the  fore-hearth  by  tapping — or 
oftener  by  breaking  through  the  plates  or  brick-work  at  some 
point — may  result  in  the  irrnption  of  some  12  to  15  tons  of 
matte  upon  the  floor  of  the  cupola-house.  The  workmen 
soon  become  expert  at  controlling  such  outbreaks  by  means  of 
dry  sand  in  unlimited  quantities — the  approach  of  anything 
wet  is  like  touching  a  match  to  a  keg  of  gunpowder — and  no 
serious  results  need  be  apprehended  when  the  buildings  are 
fire-proof,  as  should  invariably  be  the  case  where  large  brick 
furnaces  are  employed. 

Such  an  outbreak  is  treated  as  are  most  other  accidents  to 
which  this  type  of  furnace  is  liable,  by  entirely  shutting  off  the 
blast  and  allowing  everything  to  stand  quiet  for  a  few  hours. 
The  orifice  is  tightly  plugged  from  the  outside,  and  the  molten 
products  that  trickle  into  it  from  the  interior  are  allowed  to 
cool  by  standing  still,  until  it  is  as  tight  as  ever. 

The  full  burden  may  be  reached  after  feeding  two  quarter 
charges,  four  half  charges,  and  eight  three  quarter  charges 
slag  being  substituted  for  ore  to  a  considerable  extent,  until 
the  condition  of  the  furnace  warrants  the  employment  of  the 
normal  mixture. 

This  is  shown  by  the  gradual  change  of  the  color  of  the 
slag  from  a  dull  red  to  a  yellowish  white  ;  the  entire  ceasing  or 
great  diminution  of  smoke  arising  from  the  slag;  a  certain 
peculiar  viscosity  (except  in  very  basic  slags)  when  it  falls  into 
the  pot ;  a  general  brightening  of  the  tuyeres,  succeeded  by 
the  formation  of  short  noses,  perforated  abundantly  with  bright 
holes ;  and  a  steady  and  rapid  sinking  of  the  charge. 
15 


226     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

Although  the  charging  of  the  blast-furnace  is  always  one  of 
the  most  important  manipulations  belonging  to  this  apparatus, 
it  is  doubly  the  case  with  the  furnaces  now  under  discussion. 

While  the  walls  of  the  water-jacket  are  thoroughly  protected 
and  entirely  unassailable,  the  mason-work  of  the  brick  furnace 
is  completely  exposed,  and  any  error  in  the  proportion  of  fuel 
to  ore  or  in  the  manner  of  charging  is  sure  to  be  followed  by 
serious  results. 

This  is,  strange  as  it  may  seem,  peculiarly  the  case  with  a 
siliceous  charge,  and  nothing  can  more  clearly  illustrate  the 
proper  method  of  working  than  a  brief  description  of  an  irregu- 
larity that  is  constantly  liable  to  occur,  and  that  will  be  quickly 
recognized  by  all  practical  cupola  smelters. 

An  imaginary  case  will  be  assumed  where  a  newly  blown-in 
furnace,  in  good  condition,  but  with  a  slightly  too  siliceous 
charge,  begins  to  become  too  hot  in  one  end,  through  some 
slight  irregularity  of  feeding,  or  through  an  improper  propor- 
tion of  ore  to  fuel — either  too  much  or  too  little  of  the  same 
producing  very  similar  effects. 

The  attention  of  the  foreman  will  be  called  to  the  fact  that 
one  of  the  end  panels  is  becoming  very  hot,  which,  as  it  con- 
sists of  18  inches  of  fire-brick,  shows  either  that  the  inner  tem- 
perature is  much  too  high,,  or  that  the  bricks  have  already 
been  thinned  by  burning. 

A  glance  into  the  tuyere  opening  shows  that  a  heavy  black 
nose  has  already  formed,  resulting  from  the  fusion  of  the  fire- 
brick above,  which  form  a  crust  almost  impervious  to  a  steel 
bar,  and  exceedingly  infusible. 

A  consultation  with  the  man  who  feeds  that  end  of  the  fur- 
nace will  elicit  the  information  that  that  portion  of  the  charge 
is  sinking  very  slowly,  and  that  the  heat  is  rising  to  the 
surface. 

At  the  same  time,  the  blast-gauge  will  show  an  increased 
tension,  owing  to  the  blocking  up  of  the  tuyeres  that  supply 
thafe  portion  of  the  apparatus,  and  the  agglomeration  of  the 
charge  above,  owing  to  the  rapidly  ascending  temperature. 

The  already  too  siliceous  slag  is  rendered  still  more  infusible 
by  the  admixture  of  silicate  of  alumina  from  the  melting  fire- 
brick ;  and  the  high  temperature  and  powerful  reducing  atmo- 


BLAST-FURNACES  CONSTRUCTED  OF   BRICK.  227 

sphere,  resulting  from  the  almost  stationary  condition  of  this 
portion  of  the  charge,  soon  begin  to  reduce  metallic  iron  out 
of  the  slag,  and  even  from  the  matte,  the  sulphur  being  driven 
away  to  a  considerable  extent  by  the  powerful  blast,  high  tem- 
perature, and  slow  removal  of  the  molten  products. 

The  slimy,  half-fused  metallic  iron  is  soon  recognized  by  the 
bar  which  is  constantly  thrust  into  the  choked  tuyeres,  and  the 
inexperienced  metallurgist,  following  the  teaching  of  all  our  best 
text-books,  reasons  that  the  reduction  of  iron  comes  from  too 
highly  ferruginous  a  charge,  and  destroys  all  hope  of  improve- 
ment by  cutting  off  a  portion  of  the  iron  from  the  charge  fed 
into  that  end  of  the  furnace. 

This  further  diminution  of  the  oxide  of  iron,  and  conse- 
quent necessary  increase  of  temperature  to  melt  the  more  and 
more  infusible  slag,  soon  bring  about  the  exact  conditions  pre- 
vailing in  an  iron  ore  blast-furnace.  Metallic  iron  is  reduced 
in  large  quantities,  while  the  temperature  is  raised  several 
hundred  degrees,  before  the  slag — now  virtually  an  acid  sili- 
cate of  alumina  and  lime — will  become  sufficiently  softened  to 
rim  at  all.  In  the  mean  time,  the  furnace  wall,  at  the  panel,  is 
burned  nearly  through  ;  jets  of  blue  flame  appear  at  every  joint 
and  crevice,  and  the  most  superficial  examination  shows  that 
the  process  is  extending  into  one  or  the  other  of  the  corner 
columns,  threatening  the  stability  of  the  structure,  and  still 
more  alarming  the  person  in  charge.  The  column  of  ore  in 
that  end  of  the  furnace  hardly  sinks  at  all ;  the  heat  is  ascend- 
ing to  the  surface  of  the  charge  ;  and  the  general  increased 
stickiness  of  the  rapidly  lessening  slag-stream,  increase  in 
tenor  of  the  matte,  and  deposition  of  lumps  of  metallic  iron  in 
one  or  both  compartments  of  the  fore-hearth,  show  that  the 
end  is  not  far  off,  and  unfold  the  near  prospect  of  a  chilled 
furnace,  and  the  probable  presence  of  a  block  of  half-molten 
ore  and  iron  that  is  almost  impervious  to  tools,  and  may  result 
in  the  entire  abandonment  and  destruction  of  the  furnace. 

This  is  one  of  the  most  common  and  well-known  occurrences 
in  small  furnaces  and  with  inexperienced  metallurgists,  and 
might  just  as  weh1  happen  to  the  large  furnaces  now  under 
discussion,  were  it  not  fortunately  that  their  construction  and 
management  are  not  likely  to  be  undertaken  except  by  men  of 


228     MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

experience,  and  also  that,  owing  to  their  greater  size,  a  threat- 
ening— or  even  established — chill  is  much  more  easily  managed 
than  in  the  case  of  the  smaller  cupolas,  whose  contracted  shaft 
is  filled  up  solid  almost  before  one  is  aware  that  anything  is 
going  wrong. 

Owing  to  the  great  area  of  the  Orford  furnace,  a  consider- 
able portion  of  the  shaft  may  be  completely  blocked  by  a  chill, 
while  a  brisk  fusion  is  progressing  in  the  other  half,  giving  an 
opportunity,  by  the  use  of  skill  and  experience,  to  gradually 
smelt  away  the  solidified  portion  and  eventually  bring  matters 
back  to  their  normal  condition. 

Keturning  to  the  imaginary  case  that  has  just  been  followed 
to  a  disastrous  termination,  the  writer  will  endeavor  to  show 
how  such  a  catastrophe  may  be  averted,  and  will  describe  the 
course  of  events  as  they  have  occurred  scores  of  times  to 
every  practical  smelter. 

The  moment  that  it  is  noticed  that  one  end  or  corner  of 
the  furnace  is  becoming  abnormally  hot,  and  that  the  column 
of  ore  corresponding  thereto  is  sinking  slowly,  the  tuyeres 
belonging  to  that  portion  of  the  shaft — from  one  to  three  in 
number — are  immediately  removed,  and  the  openings  slightly 
plugged  with  clay.  At  the  same  time,  several  charges  of  the 
most  fusible  slag — that  from  matte  concentration  and  con- 
taining a  very  high  percentage  of  iron  is  best — are  given,  in 
place  of  ore,  and  the  whole  furnace  is  most  carefully  watched, 
to  learn  whether  the  burning  is  due  merely  to  some  local  irreg- 
ularity in  feeding,  or  whether  some  important  point  affecting 
the  whole  process  is  at  fault ;  such  as  too  much  or  too  little 
fuel  in  proportion  to  ore ;  improper  composition  of  slag ;  incor- 
rect feeding  ;  too  strong  or  too  weak  a  blast,  etc.,  etc. 

Experience  alone  can  qualify  the  metallurgist  to  quickly 
and  correctly  detect  the  cause  of  the  trouble  and  apply  the 
appropriate  remedy ;  but  in  any  case,  if,  after  taking  the  pre- 
cautions enumerated  and  waiting  a  sufficient  time  to  get  their 
full  effect,  the  burning  still  continues,  it  becomes  evident  that 
the  trouble  is  deep-seated  and  of  some  extent. 

Vigorous  measures  are  therefore  required  to  stop  the  melt- 
ing of  the  brick-work  above  the  tuyeres,  and  not  only  to  cool 
down  the  heated  end  of  the  furnace,  but  also  to  repair,  as  far 


BLAST-FURNACES   CONSTRUCTED  OF  BRICK.  229 

as  possible,  the  damage  already  done  to  the  panels — or  even 
to  the  corners  of  the  main  columns. 

Still  keeping  the*  offendiDg  tuyeres  closed  as  already  de- 
scribed, a  full  charge  of  siliceous  ore  should  be  fed  in  such 
a  way  that  it  will  sink  to  the  indicated  spot.  This  may  be 
given  either  with  or  without  coke,  or  may  be  followed  by  a 
second  or  third,  or  even  a  greater  amount,  as  the  circum- 
stances indicate ;  proceeding  with  extreme  caution,  and  allow- 
ing some  two  hours  to  intervene  between  charges. 

The  author  has  found  it  necessary  to  charge  as  much  as  11 
tons  of  almost  pure  silica — quartz  with  specks  and  veinlets  of 
carbonates  and  oxides  of  copper — into  one  corner  of  an  over- 
heated furnace,  and  this  entirely  without  coke,  before  the 
gradual  cooling  of  the  external  walls,  normal  and  even  sinking 
of  the  charge,  and  lowering  of  the  temperature  at  the  charg- 
ing-door,  indicated  that  the  mischief  had  ceased. 

The  office  of  this  siliceous  addition  is  not  to  render  the  slag 
in  general  more  siliceous.  This  would  only  bring  about  the 
evils  already  indicated,  and  probably  cause  a  heavy  reduction 
of  metallic  iron.  Its  object  is  rather  to  produce,  by  the  sud- 
den arrival  of  such  a  body  of  cold,  infusible  material,  such  an 
overwhelming  effect  as  completely  to  cool  down  that  portion 
of  the  shaft,  the  ore  itself  softening  somewhat  and  remaining 
for  the  most  part  the  corner  of  the  furnace  corresponding  to 
the  point  over  which  it  was  charged.  It  attaches  itself  to  the 
walls  and  bottom,  and  fills  up  the  cavity  caused  by  the  fusion 
of  the  fire-brick,  lowering  the  temperature  at  the  same  time  to 
a  considerable  extent,  but  producing  no  marked  effect  on  the 
general  character  of  the  slag. 

When  this  operation  is  successful,  as  is  usually  the  case, 
the  thinned  and  heated  brick-work  is  virtually  restored,  the 
deeply  excavated  bottom  is  filled  up  to  the  general  level,  and 
matters  resume  their  normal  condition,  all  irregular  bunches 
and  protuberances  of  the  siliceous  addition  that  may  have  ad- 
hered to  the  furnace  walls  becoming  gradually  melted  away 
and  smoothed  down  until  the  interior  mason-work,  if  visible, 
would  be  seen  to  have  almost  assumed  its  original  appearance. 

Such  a  result  may  seem  very  doubtful,  and,  in  fact,  the  whole 
operation  may  appear  to  partake  too  much  of  the  marvelous 


230    MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

to  those  unfamiliar  with  such  practice.  The  author  would 
hesitate  before  describing  the  foregoing  operation  as  a  matter 
of  general  every-day  occurrence,  were  it  not  that  it  can  be 
vouched  for  in  its  entirety  by  a  considerable  number  of  well- 
known  and  reliable  gentlemen.  This  practice,  as  initiated  by 
certain  members  of  the  Orford  Company,  already  mentioned, 
has  spread  until  it  is  now  a  well-known  and  recognized  part  of 
our  local  copper  metallurgy.  The  skill  attained  by  certain 
foremen  in  managing  these  very  large  furnaces  is  quite  remark- 
able, and  far  beyond  anything  described  in  this  treatise. 

While  the  imaginary  case  just  described  in  detail  represents 
only  one  of  the  various  accidents  peculiar  to  all  forms  of  blast- 
furnace, it  still  is  at  the  bottom  of  a  very  large  proportion  of 
the  instances  of  "freezing,"  "  choking-up,"  "burning-out,"  etc., 
etc.  Paradoxical  as  it  may  appear,  the  two  common  accidents 
of  "burning-out"  and  " freezing-up  "  are  closely  connected, 
and  in  reality  only  two  different  stages  of  the  same  morbid 
process.  The  young  metallurgist  cannot  overestimate  the  im- 
portance of  the  fact  that  it  is  quartz  in  one  or  another  of  its 
forms  that  is  the  most  frequent  cause  of  smelting  difficulties 
and  disasters.  Seven  out  of  the  last  eight  cases  of  metallur- 
gical difficulties  for  which  the  writer  was  called  upon  to  prescribe 
were  due  to  this  cause. 

In  spite  of  the  frequency  and  apparent  simplicity  of  this 
difficulty,  some  smelters  of  experience  never  seem  to  have 
learned  the  cause,  and  attribute  the  slow  and  irregular  run- 
ning of  the  cupola  and  the  frequent  filling  up  of  the  crucible 
with  sows  to  "  too  much  iron  in  the  charge  " — "  too  much  sul- 
phur " — "  magnesia  in  the  limestone  flux,"  etc.,  when,  in  almost 
every  instance,  a  mere  ocular  examination  of  the  slag  is  suffi- 
cient to  show  that  silica  is  at  the  bottom  of  the  trouble.  No 
apology  is  needed  for  emphasizing  this  point,  when  men  con- 
sidered as  expert  metallurgists  are  constantly  falling  into  this 
error. 

It  is  especially  during  such  accidents  and  irregularities  that 
the  great  advantages  of  these  very  large  furnaces  become  fully 
apparent.  "Where  a  small  shaft  would  soon  be  completely  and 
irretrievably  choked,  necessitating  the  great  expense  of  blow- 
ing down  and  subsequently  chiseling  out  the  half-fused  mass  of 


BLAST-FURNACES   CONSTRUCTED  OF    BRICK.  231 

ore  and  cinder,  no  large  furnace,  in  any  instance  known  to  the 
author,  has  ever  become  so  blocked  up  and  filled  with  a  chill 
that  it  has  not  been  quite  easy  to  save  it  by  using  appropriate 
means.  Even  though  one  end  be  completely  blocked,  there  is 
always  ample  space  at  some  points  of  its  eleven-foot  shaft  to 
permit  the  descent  of  the  charge  and  retain  a  sufficient  number 
of  tuyeres  intact  to  gradually  melt  out  the  chill  and  restore  the 
shaft  to  something  like  its  former  dimensions.  Some  consid- 
erable irregularity  of  form  naturally  results  from  repeated 
manipulations  of  this  kind  ;  but  so  long  as  sufficient  area  re- 
mains at  the  tuyere  level,  and  no  projecting  masses  impede  the 
regular  descent  of  the  charge,  no  diminution  of  capacity  need 
follow,  nor  increase  of  difficulty  in  managing  the  furnace. 

The  accompanying  sketch  gives  a  tolerably  correct  view  of 
the  shape  of  one  of  these  large  brick  furnaces  at  the  tuyeres 


The  rectangle  shows  the  shape  before  the  campaign ;   the  irregular 
line,  after  the  campaign. 

upon  its  blowing  out  for  repairs  after  a  continuous  campaign 
of  8J  months,  during  which  time  over  18,000  tons  of  exceed- 
ingly ferruginous  ore  were  smelted  in  it,  yielding  a  very  low 
grade  matte  and  a  slag  averaging  about  22  per  cent,  silica  and 
over  70  per  cent,  protoxide  of  iron.  As  it  is  drawn  to  a  scale, 
the  extent  of  the  irregularity  is  easily  appreciable,  the  original 
dimensions  being  3  feet  3  inches  by  11  feet  4  inches. 

In  fact,  the  full  capacity  of  this  type  of  furnace,  when 
smelting  a  basic  ore,  is  not  reached  until  the  walls  are  burned 
out  to  a  considerable  extent,  which  may  indicate  the  policy  of 
widening  the  furnace  in  the  first  place.  When  smelting  a 
siliceous  ore,  or  when  a  large  proportion  of  fines  is  present,  the 
gain  in  width  is  accompanied  with  a  decrease  of  temperature 


232      MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

and  irregularities  in  the  descent  of  the  charge — circumstances 
that  soon  rectify  the  trouble  by  adhering  to  the  walls,  and  fill- 
ing up  the  shaft  again  with  a  rapidity  that  may  be  disastrous 
if  not  observed  and  remedied  in  time. 

As  has  been  already  briefly  mentioned,  the  cutting  down 
of  the  bottom  and  piercing  of  the  foundation-walls  is  an  acci- 
dent that  sometimes  occurs,  although  usually  only  when  the 
charge  consists  of  a  very  fusible  unroasted  ore,  producing  a 
matte  of  low  grade — from  25  per  cent,  downward,  whose  fiery 
and  corrosive  qualities  are  well  known  to  all  furnace  men.  It 
is  to  the  great  quantity,  as  well  as  corrosive  quality,  of  this 
substance,  and  this  usually  in  connection  with  a  basic  slag, 
that  this  destructive  process  is  due  ;  and  in  spite  of  much  care 
and  expense  bestowed  on  the  matter,  no  material  has  yet  been 
found  that  will  withstand  a  daily  production  of  from  20  to  45 
tons  of  this  intractable  product.  But  a  means  of  greatly  lessen- 
ing its  destructive  action,  as  well  as  of  greatly  prolonging  the 
life  of  the  entire  structure  and  rendering  its  management  much 
easier,  has  been  discovered  and  quite  generally  adopted,  being 
first  brought  into  notice  by  Mr.  John  Thomson,  of  the  Orford 
Company.  It  consists  in  duplicating  the  furnace  plant  and 
running  each  individual  cupola  only  ten  or  twelve  hours  of  the 
twenty-four.  This  is  a  scheme  that  seldom  recommends  itself 
to  one  on  first  hearing,  but,  after  a  thorough  trial,  will  be 
found  to  possess  numerous  important  advantages,  whiTe  its  only 
drawback  is  the  increased  first  cost  of  the  plant — a  trifling  con- 
sideration in  comparison  with  the  large  interests  usually  at 
stake. 

A  mere  doubling  of  the  cupola  plant  is  sufficient  to  over- 
come the  difficulties  mentioned ;  but  if  it  be  desired  to  reap 
the  full  advantages  of  the  scheme,  a  corresponding  increase 
should  be  made  in  the  blast  apparatus.  This  being  effected, 
the  entire  smelting  process  may  be  confined  to  the  daytime, 
avoiding  the  difficulties  and  drawbacks  of  night  work,  saving 
the  wages  of  one  or  more  foremen,  and  rendering  it  possible 
for  the  manager  to  retain  that  complete  personal  oversight 
of  the  smelting  process  that  is  unattainable  when  half  of  it  is 
concealed  from  his  inspection.  If  this  were  the  only  benefit 
derived  from  the  above  plan,  it  would  in  most  cases  be  well 


BLAST-FURNACES  CONSTEUCTED   OF  BRICK.  233 

worthy  of  adoption ;  but  the  advantages  accruing  to  the 
furnaces  themselves,  as  well  as  to  the  entire  process,  are  too 
numerous  and  far-reaching  to  be  thoroughly  explained  in  this 
treatise. 

In  the  first  place,  the  cutting  down  of  the  furnace  bottom 
is  usually  completely  remedied  by  the  long  and  ever-recurring 
periods  of  complete  repose,  during  which  the  thinned  brick- 
work is  again  sealed  by  the  chilling  of  the  molten  products  ; 
the  hearth  is  renewed  by  the  solidification  of  the  matte  and 
slag  still  remaining  in  the  cavities  of  the  hearth ;  the  over- 
heated brick-work  cools  from  the  outside  to  such  an  extent 
that  the  area  that  to-day  has  given  constant  annoyance  by  its 
obstinate  burning,  with  the  constant  threat  of  finally  breaking 
through  and  causing  serious  trouble,  will  to-morrow  be  found 
as  cool  as  or  cooler  than  any  other  portion,  owing  to  the  thin- 
ness of  its  walls  ;  and  various  slight  difficulties  that  are  pretty 
sure  to  occur  in  the  course  of  a  long  run  are  averted  before 
they  become  of  importance,  while  the  trouble  begins  at  a  new 
point,  only  to  be  again  averted  before  it  has  gained  serious 
headway.  This  is  by  no  means  an  uncommon  or  imaginary 
case,  but  a  matter  of  frequent  occurrence,  and  these  lines  are 
written  after  several  years'  trial  of  both  the  constant  and  in- 
termittent method  of  smelting ;  the  experience  of  others  who 
have  fairly  tried  this  plan,  in  connection  with  large  brick  fur- 
naces, being  equally  favorable. 

The  writer's  attention  was  first  called  to  this  matter  in  1871 
when  noticing  the  almost  invariable  improvement  in  behavior 
and  capacity  that  succeeded^any  accidental  stoppage  of  cupola- 
furnaces  that  he  was  then  managing.  The  ores  were  exceed- 
ingly bad  and  siliceous,  and  the  difficulties  detailed  in  the  pre- 
ceding pages  followed  each  other  with  disheartening  regularity 
and  frequency.  Great  pains  were  taken  to  secure  a  steady 
and  uninterrupted  run,  fears  being  entertained  that  any  stop- 
page would  be  disastrous  to  the  furnace  in  the  more  or  less 
critical  condition  that  seemed  to  be  its  normal  state  ;  but  after 
finding  that  the  benefits  following  any  temporary  stoppage  of 
the  machinery  had  become  so  obvious  that  the  foreman  was  in 
the  habit  of  purposely  causing  slight  accidents  in  order  to  help 
his  furnace  out  of  some  particularly  critical  situation,  it  was 


234     MODERN  AMERICAN  METHODS  OF  COPPER  SMELTING. 

decided  to  adopt  the  practice  of  stopping  for  two  or  three 
hours  whenever  the  ordinary  incidents  of  burning  out,  etc.,  be- 
came unusually  critical.  This  habit  was  carried  farther  and 
farther,  proceeding  with  caution  and  gradually  lengthening  the 
stoppages,  until  it  came  to  be  considered  an  almost  universal 
remedy,  and  was  as  often  applied  for  chilling  or  freezing  up  as 
for  the  opposite  condition  of  affairs,  and  no  misfortune  ever 
arose  from  its  reasonable  application. 

This  practice,  like  every  other,  must  be  used  with  care  and 
judgment,  and  may  easily  be  carried  to  an  extreme,  but  as  a 
rule  is  the  least  dangerous  measure  that  can  be  adopted  with 
a  badly  acting  furnace  of  large  area.  A  small  furnace  might 
easily  chill  in  a  few  hours,  so  that  the  length  of  the  period  of 
repose  must  be  proportioned  to  the  size  of  the  shaft  and  to 
the  cubic  contents  of  the  heated  material.  The  thickness  of 
the  walls  must  also  be  considered,  as  the  rapidity  of  the  es- 
cape of  heat  depends  upon  the  thickness  of  the  brick-work.  It 
is  hardly  necessary  to  say  that  every  orifice  and  crevice  about 
the  furnace  must  be  tightly  sealed,  the  tuyeres  being  removed, 
and  their  openings,  as  well  as  the  slag -run,  being  tightly  filled 
with  damp  clay,  while  the  brick- work  in  their  vicinity  must  be 
searched  for  possible  cracks,  and  all  such  openings  carefully 
plastered  over.  Otherwise,  the  incoming  currents  of  air 
would  gradually  burn  away  all  the  fuel  contained  in  the  charge, 
leaving  the  furnace  in  a  hopeless  condition.  If  it  is  to  stand 
still  any  length  of  time,  such  as  over  night,  a  few  extra 
charges  of  coke  should  be  given  an  hour  or  two  before  stop- 
ping, so  that  there  may  be  an  abundance  of  fuel  in  the  bottom 
of  the  furnace.  A  small  charge  of  basic  slag  should  also  be 
given ;  and  as  soon  as  the  blast  is  taken  off,  the  basin  or 
fore-hearth  tapped,  and  all  openings  sealed,  the  surface  of  the 
charge  should  be  covered  with  a  layer  of  fine  coke,  over  which 
is  spread  an  inch  or  two  of  fine,  fusible  ore.  The  slag-hole  con- 
necting the  furnace  with  the  fore-hearth  should  be  thoroughly 
cleared  out ;  the  layers  of  chilled  slag  and  ashes,  by  which  the 
blowing  through  of  the  blast  is  prevented,  removed,  and  the 
channel  itself  filled  with  fine  charcoal  or  coke,  well  rammed  in 
with  a  "  stopping  pole."  This  is  rendered  impervious  to  air  by 
an  exterior  plug  of  clay,  and  the  fore-hearth,  while  still  hot, 


BLAST-FUKNACES   CONSTRUCTED   OF  BEICK.  235 

being  scraped  clean  of  all  half-fused  masses  of  slag  or  reduced 
iron,  and  every  tiling  being  prepared  for  the  morrow's  work,  the 
cupola  may  be  left  in  charge  of  an  experienced  watchman — 
preferably  an  old  smelter.  On  the  ensuing  morning,  a  light 
blast  is  put  on,  and  the  channel  being  cleared  out,  slag  will 
flow  in  from  five  to  ten  minutes,  while  in  half  an  hour  the  fur- 
nace will  be  in  normal  condition,  and  in  most  cases  smelting 
more  rapidly  and  satisfactorily  than  when  left  the  previous 
evening. 

The  extreme  length  of  time  that  a  large  furnace  may  stand 
in  this  way  without  injury  is  unknown  to  the  author.  Much 
depends  on  the  fusibility  of  the  charge,  the  character  of  the 
fuel,  the  more  or  less  perfect  exclusion  of  all  air,  and  probably 
also  upon  the  quality  and  amount  of  sulphide  compounds 
present,  whose  gradual  oxidation  may  sustain  the  vitality  of  the 
charge  for  a  much  greater  length  of  time  than  if  absent.  The 
following  instances,  from  personal  experience,  show  that  a 
considerable  delay  is  permissible. 

A  furnace  running  on  a  fusible  charge  of  calcined  pyritic 
ore  was  shut  down  Friday  noon,  on  account  of  an  accident 
to  the  engine.  Further  examination  showed  the  accident  to 
be  of  such  a  nature  as  to  cause  a  delay  until  the  succeeding 
Wednesday  night — 5|  days — at  the  end  of  which  time,  a  light 
blast  was  applied  without  much  hope  of  a  favorable  result, 
although  the  coke  on  top  of  the  charge  was  hot  and  glowing. 

There  seemed  a  good  deal  of  obstruction  to  the  blast  at 
first ;  but  in  twenty  minutes,  a  cold,  thick  slag  began  to  run, 
which  gradually  improved,  until  the  furnace  resumed  its  normal 
condition  and  capacity  in  about  eight  hours.  The  charge  had 
sunk  about  two  feet  in  the  furnace  during  this  period  of  repose. 
The  grade  of  the  first  tap  of  matte  (the  siphon-tap  being  im- 
practicable in  this  condition  of  affairs)  was  46  per  cent.,  the 
ordinary  average  being  from  28  to  29  per  cent.  The  succeed- 
ing tappings  gradually  decreased — going  successively  42,  37, 
and  34  per  cent.,  the  normal  grade  being  reached  soon  after 
the  furnace  had  regained  its  usual  capacity. 

Periods  of  4  days,  3|,  3J,  3,  and  of  less  time,  appear  in  the 
writer's  notes,  the  only  serious  accident  occurring  during  one 
of  the  shorter  periods,  from  the  falling  out  of  two  of  the  tuyere- 


236     MODERN  AMEEICAN  METHODS  OF  COPPER  SMELTING. 

plugs,  whereby  a  current  of  air  entered  the  furnace  for  twelve 
hours  before  being  discovered.  The  coke  was  completely 
burned  out  of  the  lower  portion  of  the  charge  for  about  two- 
thirds  of  that  part  of  the  shaft  nearest  the  opening ;  but  the 
furnace  was  eventually  saved  by  blowing  lightly  into  three 
tuyeres  at  the  opposite  end,  which  were  still  supplied  with 
fuel,  and  little  by  little  smelting  out  the  entire  half-fused  block 
of  charge.  Much  benefit  was  derived  by  introducing  coke  into 
the  furnace  through  such  tuyeres  as  seemed  to  warrant  the 
trouble.  Owing  to  the  great  size  of  the  tuyere  openings  (6 
inches),  this  was  easily  effected,  and  the  smelting  much  facili- 
tated. In  fact,  if  any  cavity  in  the  semi-fused  mass  could  have 
been  found  at  any  point  accessible  to  the  blast,  nothing  would 
have  been  simpler  than  to  break  a  hole  through  one  of  the 
brick  panels  and  fill  the  opening  with  coke.  The  author  has 
done  this  in  later  instances  with  very  satisfactory  results,  a 
cavity  opposite  the  tuyeres  having  been  formed  by  dragging 
out  a  lot  of  the  stock,  from  which  the  coke  had  burned  so 
gradually  as  not  to  fuse  it. 

Space  is  wanting  for  a  description  of  the  use  of  petroleum, 
gas,  and  other  concentrated  fuels  for  similar  purposes,  as  the 
writer's  own  experience  with  such  measures  has  been  entirely 
unsatisfactory,  nor  can  he  find  any  record  of  successful  cases 
in  the  annals  of  American  copper  smelting. 

The  most  Herculean  efforts  are  warrantable  when  any 
reasonable  probability  exists  of  the  saving  of  an  iron  furnace 
from  complete  chilling  up ;  but  in  copper  smelting,  the  com- 
parative cheapness  and  simplicity  of  the  structure  itself,  and 
the  certainty  of  being  able  to  remove  the  worst  chill  by 
mechanical  means  in  a  comparatively  short  time,  render  such 
unusual  and  expensive  measures  less  important. 

The  oxidation  of  the  sulphides  in  the  charge  during  the 
period  of  repose  is  an  element  of  some  importance,  although 
seldom  so  striking  as  in  the  case  just  mentioned.  Still,  the 
closing  down  of  the  cupola  over  night  is  invariably  accompanied 
with  a  perceptible  rise  in  the  grade  of  the  matte  produced 
during  a  certain  period  succeeding  ;  being  greatest  at  first,  and 
gradually  diminishing  as  the  contents  of  the  furnace  are  re- 
placed with  fresh  ore.  This  increase  in  richness  is  at  first 


BLAST-FURNACES   CONSTRUCTED  OF  BRICK.  237 

seldom  less  than  5  per  cent,  diminishing  rapidly,  however,  as 
the  ore  nearest  the  bottom  of  the  charge  seems  to  have  experi- 
enced the  most  thorough  oxidation. 

Though  apparently  a  trivial  matter,  this  enrichment  of  the 
matte  is  a  direct  pecuniary  gain,  and  according  to  a  rough 
estimate,  will  offset  the  interest  on  the  capital  necessary  for 
the  double  plant  several  times  over  in  the  course  of  a  year. 

Another  useful  and  frequently  applied  remedy  for  various 
irregularities  in  cupola  smelting  is  the  so-called  "running- 
down  "  of  the  furnace,  by  which  is  meant  a  mere  cessation  of 
charging  until  the  column  of  ore  and  fuel  has  sunk  to  a  point 
far  below  its  normal  limits.  The  shaft  is  then  rapidly  filled 
with  the  usual  alternate  charges  of  ore  and  fuel,  and  every 
thing  goes  on  as  before. 

"Without  attempting  to  explain  the  reason  therefor,  it  is 
certain  that  this  practice  is  sometimes  of  great  advantage, 
obstinate  irregularities  often  being  conquered  thereby,  and  the 
normal  condition  of  things  resumed.  It  is  especially  useful 
when  it  is  desired  to  create  a  sudden  and  profound  lowering  of 
temperature  at  some  point  where  a  serious  localized  burn- 
ing is  taking  place ;  for  the  exposure  of  the  naked  inclosing 
walls  of  the  shaft  renders  it  possible  to  deposit  the  batch  of 
ore  that  is  used  to  cool  the  walls  in  the  exact  spot  where  it  is 
needed ;  and  it  is  possible  to  use  for  this  purpose,  under  such 
circumstances,  an  easily  fusible  ore  or  slag,  instead  of  the 
highly  siliceous  material  that  is  usually  selected  when  this 
process  of  cooling  down  is  undertaken  blindly  from  above. 

Wall  accretions  may  also  be  reached  in  this  manner,  the 
charge  being  allowed  to  settle  until  they  are  exposed,  where- 
upon they  may  be  removed  by  a  long  bent  steel  bar  introduced 
through  one  of  the  charging-doors,  the  glowing  interior  being 
cooled  down,  if  necessary,  by  sprinkling  with  water. 

Still  another  means  of  remedying  the  cutting-down  of  the 
furnace  bottom  has  been  mentioned  in  a  former  section,  but  is 
sometimes  useful  in  connection  with  the  large  brick  furnace. 
This  is,  the  introduction  of  ore  or  sand  through  the  tuyere 
openings,  which,  being  both  cold  and  the  latter  infusible,  will 
not  combine  with  the  slag,  as  it  is  already  below  the  smelting 
zone  ;  but  will  simply  remain  in  place  and  assist  in  building 


238     MODERN"  AMEEICAN  METHODS   OF   COPPEE  SMELTING. 

up  a  new  bottom.  By  this  means,  even  the  molten  masses 
present  may  be  partially  solidified  and  a  great  advantage 
gained  in  a  short  time.  The  author  has  occasionally  tried  the 
introduction  of  water  in  the  same  manner  and  for  the  same 
purpose,  taking  as  a  guide  the  very  decided  local  chilling  pro- 
duced by  a  leaky  water-jacket ;  but  the  results,  though  locally 
satisfactory,  are  not  sufficiently  extended,  while  the  operation 
itself,  especially  in  connection  with  a  low-grade  copper  matte, 
cannot  be  recommended  to  any  who  object  to  certain  and 
frequent  explosions  of  considerable  force. 

In  connection  with  the  measures  already  detailed  for  keep- 
ing the  furnace  in  proper  condition,  may  be  mentioned  the  ex- 
ternal repairs  that  it  is  feasible  to  execute  while  the  furnace  is 
still  in  blast.  Not  all  smelters  are  aware  of  the  very  extensive 
repairs  that  may  be  carried  out  without  stopping  the  blast 
more  than  a  few  hours  ;  the  length  of  the  campaign  often  being 
doubled  by  the  construction  of  a  new  panel,  the  repairing  of  a 
pillar,  and  other  familiar  and  inexpensive  operations.  These 
are  of  too  extensive  and  varied  a  nature  to  be  enumerated  in 
detail ;  but  a  few  of  the  teachings  of  experience  will  throw 
some  light  on  the  practice  in  general. 

The  replacement  of  one  or  more  panels  that  have  become 
so  thin  as  to  threaten  a  constant  breaking  through  of  the 
charge  is  a  simple  though  very  hot  and  laborious  task. 

All  needful  material  for  the  renewal  being  prepared  and 
collected  on  the  spot,  the  blast  is  shut  off,  the  fore-hearth  tap- 
ped, and  the  condemned  brick-work  at  once  broken  in  with 
sledge  and  bar.  So  much  of  the  glowing  charge  as  is  neces- 
sary is  at  once  dragged  out  of  the  opening  with  long  hoes  and 
rakes,  and  sprinkled  with  water  so  that  the  men  can  stand  on 
it  to  work. 

When  the  bricks  have  been  removed  to  the  extent  deemed 
necessary,  the  cavity  left  in  the  column  of  stock  is  quickly  filled 
with  dampened  coke,  a  few  wooden  slats  being  wedged  across 
the  opening,  to  keep  the  fuel  from  falling  out. 

The  most  important  measure  is  to  obtain  a  solid  founda- 
tion for  the  new  wall,  and  to  accomplish  this,  all  accretions  of 
slag  and  metal  of  which  the  old  wall  largely  consisted,  must  be 
chiseled  away  until  sound  brick-work  is  reached,"  which  being 


BLAST-FURNACES    CONSTRUCTED  OF  BRICK.  239 

leveled  with  thick  fire-clay,  offers  a  proper  starting-point.  The 
work  must  proceed  with  great  rapidity,  as  the  passage  of  air 
through  the  opening  will  soon  consume  the  fuel  in  the  charge. 
Little  attention  is  paid  to  neatness  or  even  regularity  so  long 
as  strength  and  tightness  are  obtained.  If  the  work  promises 
to  occupy  more  than  two  or  three  hours,  the  opening  should  be 
closed  at  the  beginning  by  a  thin  plate  of  sheet-iron  tightly 
cemented  at  the  edges  with  clay,  outside  of  which  the  new 
wall  is  raised.  When  all  is  completed,  the  sheet-iron — unless 
already  consumed — is  cut  away  opposite  the  tuyere  openings, 
and  the  blast  is  put  on  at  once,  there  being  no  necessity  of 
waiting  for  the  work  to  dry,  as  the  heat  from  the  furnace  will 
evaporate  all  moisture  quite  as  soon  as  is  desirable. 

By  this  means,  extensive  repairs  may  be  executed  on  any 
portion  of  the  furnace,  it  being  even  possible  to  put  in  a  new 
bottom  or  repair  the  foundation  walls,  by  suspending  the 
charge  on  bars  driven  transversely  through  the  furnace. 
When  possible,  the  ashes  of  the  rapidly  consumed  fuel  should 
be  cleared  out  before  starting  again  ;  but  there  are  but  few  in- 
stances where  it  will  not  be  found  better  to  blow  out  the  fur- 
nace when  such  radical  repairs  are  required. 

The  water-jacket  furnace  may  also  be  allowed  to  stand  idle 
much  longer  than  is  usually  supposed,  as  the  absence  of  air 
prevents  the  combustion  of  the  fuel ;  but  the  rapid  conduction  of 
heat  through  its  cold  metallic  walls  prevents  any  such  liberties 
as  may  be  taken  with  the  brick  furnace,  and  renders  it  unsafe 
to  leave  the  furnace  more  than  twelve  hours.* 

In  fact,  it  is  better  to  run  the  charge  down  to  the  very  bot- 
tom, throw  in  a  few  baskets  of  coke,  and  after  stopping  ah1  the 
air-holes,  leave  the  jacket  in  this  condition,  by  which  all  dan- 
ger of  chilling  is  avoided,  and  the  bottom  being  kept  hot, 
smelting  may  be  resumed  in  a  very  short  time. 

The  final  blowing  out  of  the  large  furnace  presents  no 
peculiar  features.  The  blast  should  be  lessened  as  the  charge 
sinks,  and  as  soon  as  slag  stops  running,  the  breast-wall,  and, 
if  expensive  repairs  are  imminent,  some  of  the  rear  and  end 

*  Since  writing  this  paragraph,  experience  has  taught  me  that  water- 
jackets  can  be  allowed  to  stand  overnight  with  as  good  results  as  in  the  case 
of  brick  furnaces,  and  by  employing  the  same  precautions. 


240     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

panels,  should  be  knocked  in,  and  all  stock  and  fuel  dragged 
out,  until  a  tolerably  even  bottom  is  reached,  which  needs  no 
preparation  for  the  succeeding  campaign. 

Any  burning  out  of  the  brick  pillars  that  form  the  main 
support  of  this  furnace,  should  be  carefully  watched  and  re- 
paired before  it  has  proceeded  to  a  dangerous  extent.  This 
burning  is  sometimes  so  obstinate  that  when  it  is  important 
not  to  stop  the  furnace  or  blow  out,  it  is  necessary  to  support 
the  superincumbent  brick-work  with  props  and  braces,  which 
should  remain  in  place  until  the  pillars  have  been  restored  to 
their  former  strength. 

Estimates  of  the  cost  of  both  building  and  running  one  of 
these  large  brick  furnaces  of  the  Orford  type  will  be  found  in 
this  chapter. 

Similar  estimates  for  the  small  brick  furnaces  formerly  used 
at  Ely,  Ducktown,  Ore  Knob,  and  elsewhere,  do  not  come  with- 
in the  scope  of  this  work,  which  treats  of  modern  rather  than 
of  historical  methods.  The  cost  of  smelting  in  the  small  fur- 
naces was  from  three  to  six  times  as  great  as  in  those  now  in 
use. 

There  remains  to  be  still  considered  the  application  of 
w.ater  tuyeres  and  other  cooling  devices  to  furnaces  con- 
structed of  brick  or  stone. 

The  author's  own  experience  is  entirely  in  favor  of  the  em- 
ployment of  properly  constructed  iron,  or  better,  bronze  or 
copper  tuyeres,  containing  a  space  for  the  introduction  of 
water.  In  Colorado  and  other  places,  he  has  used  water  tuy- 
eres with  invariable  satisfaction,  the  only  drawback  being  the 
frequent  cracking  of  the  cast-iron,  which  is  now  overcome. 

While  they  offer  little  or  no  protection  to  the  furnace  wall, 
they  are  indestructible  themselves,  and  by  delivering  the  wind 
at  a  fixed  point,  even  though  the  walls  may  be  eaten  away  all 
about  them  to  the  depth  of  a  foot  or  more,  they  remove  the 
point  of  greatest  heat  from  the  wall  itself  and  practically 
retain  the  smelting  area  at  the  same  invariable  size,  the  latter 
being  practically  bounded  by  vertical  planes  passing  through 
the  nozzles  of  the  tuyeres. 

It  is  also  possible,  if  desirable,  to  project  them  into  the  in- 
terior of  the  furnace  to  a  distance  of  several  inches  from  the 


BLAST-FURNACES   CONSTRUCTED  OF  BRICK.  241 

walls.  Although  this  practically  diminishes  the  size  of  the 
smelting  area,  it  saves  the  walls  from  burning,  and  in  case  of 
a  weak  blast  or  of  an  unusually  dense  charge  arising  from  a 
large  proportion  of  fine  ore,  may  render  practicable  the  smelt- 
ing of  material  that  would  be  impossible  under  other  circum- 
stances. 

They  were  tried  on  the  first  large  Orford  furnaces,  but 
failed,  owing  to  the  severity  of  the  winter  and  other  accidental 
causes,  rather  than  from  any  fault  due  to  the  tuyeres  them- 
selves. Their  construction  and  management  are  too  familiar 
to  require  further  explanation  in  these  pages. 

The  surface  cooling  of  the  brick -work  by  means  of  a  spray 
of  water  on  the  outside  has  been  tried  on  many  occasions  and 
with  various  forms  of  apparatus.  It  has  rarely  given  satisfac- 
tion, and  in  the  writer's  opinion  is  as  dangerous  and  worthless 
a  device  as  can  well  be  imagined. 

To  those  familiar  with  the  results  of  contact  between  water 
and  molten  matte,  it  is  not  necessary  to  bring  up  any  further 
arguments  to  condemn  a  device  that  can  only  be  accompanied 
by  a  constant  wetting  of  everything  in  the  vicinity  of  the  fur- 
nace. 

Besides,  the  idea  itself  is  an  extremely  faulty  one,  as,  owing 
to  the  non-conductivity  of  fire-brick,  a  wall  less  than  a  foot 
thick  may  continue  melting  on  one  side,  while  its  other  sur- 
face is  constantly  sprayed  with  cold  water. 

All  devices  of  this  kind,  in  which  the  water  comes  in  con- 
tact with  the  free  exterior  surface  of  the  furnace  wall,  are,  in 
the  author's  opinion,  worse  than  useless,  and  likely  to  be  accom- 
panied by  most  dangerous  results. 

ESTIMATE    OF    COST  OF    LARGE    BRICK    BLAST-FURNACE. 

Excavation  for  foundation  :  1,000  cubic  feet  at  8  cents $80.00 

Foundation  of  beton 65.00 

Cubic  feet. 

Total  fire-brick  for  furnace  proper 1,640 

Lining  for  cross-flue  and  down -take 540 

Fore-hearth,  etc 45 

Total 2,225 

Carried  forward $14o.OO 

16 


242       MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

Brought  forward $145.00 

At  18  brick  per  cubic  foot  =  40,050  at  $40  a  thousand 1,602.00 

Red  brick  for  down-take  and  flue  :  16,800  at  $8 134.40 

6i  tons  fire-clay  at  $8 52.00 

6  casks  lime  at  $1.50 9.00 

2  tons  sand  at  $1.50. 3.00 

Old  rails  for  binders  :  180  yards  at  80  pounds  a  yard  = 

14,400  pounds  at  $  cent 108.CO 

Tie-rods   for    furnace,   flue,    and   down-take  :   620     Pounds. 

feet  of  1£  iron  =  2,480  pounds 2,480 

Loops,  nuts,  etc 166 

Angle  iron  for  down-take 172 

Wrought-iron  rods,  etc.,  about  fore-hearth 66 

Total 2,884 

At  2  cents  a  pound 57.68 

Castings  :  Pounds. 

3  feed-door  frames 792 

Damper  and  frame 455 

Plates  for  fore-hearth 560 

Slag  and  matte-spouts. 80 

Plates  for  charging-floor 1,260 

Miscellaneous 420 

Total 3,567 

At  21  cents  a  pound 89.17 

Material  and  labor  for  arch  patterns  and  other  carpenter 

work 32.40 

Labor  : 

Mason,  88  days  at  $4 352.00 

Ordinary  labor,  102  days  at  $1.50 153.00 

9£  days  smith  and  helper 47.50 

Blast-pipe  and  tuyeres 136.00 

Cloth  for  tuyere  bags  and  labor 3.80 

Superintendence 120.00 

Miscellaneous  . .  65.00 


Grand  total $3,109.95 

Tools  essential  to  furnace,  steel  and  iron  bars,  shovels,  rakes, 

hammers $55.90 

15  slag-pots  at  $13.50 202.50 

4  iron  borrows  at  $9 36.00 

Manometer 2.50 


Total $296.90 

The  above  estimate  is  exclusive  of  main  blast-pipe,  blower, 
motive  power,  hoist,  and  chimney  or  dust-chambers ;  the  al- 
lowance for  cross-flue  and  down-take  being  sufficient  to  cover 


BLAST-FURNACES   CONSTRUCTED   OF  BRICK.  243 

cost  of  chimney  in  those  exceptional  cases  where  no  provision 
is  made  for  catching  the  immense  amount  of  flue-dust  gener- 
ated in  this  method  of  smelting. 

A  compact  and  economical  hoist  and  ample  provision  for  a 
large  charging-floor  and  generous  bin  room  are  essential  to 
convenient  and  economical  work. 

ESTIMATE  OF  COSTS  OF  CUPOLA  SMELTING. 

Details  of  expense  of  running  a  42-inch  circular  water- 
jacket  cupola,  smelting  56  tons  of  fusible  ore  per  24  hours.* 

As  it  may  be  a  matter  of  interest  to  many  to  compare  the 
cost  of  copper  smelting  in  Arizona,  Montana,  and  other  remote 
districts  with  the  cheaper  scale  of  prices  assumed  for  our 
standard,  this  information  is  given  in  a  second  column.  These 
figures  refer  to  works  situated  near  a  line  of  railroad,  and  of 
large  capacity,  as  the  smelters  at  a  distance  from  travel  must 
frequently  pay  double  or  even  treble  the  amount  given  for  coke 
and  other  supplies,  while  the  cost  of  running  a  single  furnace 
is  proportionately  much  greater. 

PER  TWENTY-FOUR  HOUR8. 

Fuel  and  Supplies.                                   .  East.  Arizona. 

Eight  tons  coke $40.00  $200.00 

Fuel  for  blast  and  attendance 7. 50  1(5 . 00 

Clay  and  sand .60  1 .50 

Five  tons  limestone  (or  other  flux) 7.50  15.00 

Cost  of  pumping  water  for  jacket 4 . 80  1 1 . 50 

Oil,  lights,  etc 3.50  9.00 

Renewal  of  tools,  pots,  molds,  etc 2.25  4.60 

Repairs  on  furnace  and  machinery 2.00  4.10 

Proportion  of  cost  of  blowing-in  and  out .40  .85 

Sinking  fund  to  replace  furnace,  etc 1 .65  2.95 

Miscellaneous 4.00  11.00 

$74.20        $276.50 

*  These  estimates,  both  of  construction  and  smelting,  are  taken  from  the 
results  of  actual  work,  not  being  drawn  exclusively  from  any  one  establish- 
ment, but  being  the  average  results  of  several  successful  works  representing 
advanced  American  practice. 

It  must  not  be  forgotten  that  several  of  the  heaviest  items  that  go  to  make 
up  the  running  expenses  of  all  metallurgical  establishments  are  necessarily 
omitted.  These  are  the  general  expenses  and  salaries  ;  extraordinary  expen- 
ses arising  from  accidents  ;  cost  of  experimental  work,  and  similar  matters, 
which  may  aggregate  a  very  large  amount. 


244     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 


Labor  (per  twenty-four  hours). 

East. 
$10.00 

Arizona. 
$15.00 

7.00 

13.00 

5.00 

10.00 

3.00 

6.00 

1.25 

3.50 

2.00 

7.00 

Proportion  of  superintendence  , 

3  20 

10.50 

Fuel  &nd  supplies            

$31.45 
74  20 

$65.00 
276  50 

Total $105.65       $341.50 

Costing  respectively  per  ton $1 .88|-         $6.10 

To  which  should  be  added  5  per  cent,  for  resmelting  foul  slag 
and  flue-dust,  increasing  the  final  cost  to  $1.98  and  $6.40  a  ton. 
Nothing  is  allowed  for  transporting  ore  to  the  furnace  and 
many  other  items,  which  only  obscure  an  estimate  supposed 
to  refer  to  the  cost  of  running  a  furnace  as  part  of  a  larger 
plant. 

If  the  entire  expense  of  the  works  were  supported  by  a 
single  smelting-furnace,  the  estimate  would  be  so  complicated 
and  the  cost  of  smelting  so  high  as  to  create  an  entirely  false 
impression.  Such  instances  occur,  however,  though  only 
financially  successful  under  exceptionally  favorable  conditions 
and  with  abundant  and  high-grade  ores. 

The  following  estimate  of  the  cost  of  smelting  a  fusible  ore 
in  the  large  brick  furnace  so  often  referred  to  is  also  based 
upon  the  same  conditions,  the  furnace  being  supposed  to  be 
only  a  portion  of  a  large  plant,  and  only  to  be  charged  with  its 
own  share  of  the  cost  of  power,  superintendence,  etc.,  etc. 

The  ore  is  supposed  to  be  a  low-grade,  roasted  pyrites,  or 
some  other  equally  fusible  and  self-fluxing  material.  It  is 
assumed  that  the  furnace  makes  campaigns  of  nine  months, 
smelting  daily  95  tons  of  ore. 


BLAST-FURNACES   CONSTRUCTED   OF  BRICK.  245 
ESTIMATE. 

Fuel  and  supplies : 

12i  tons  coke,  at  $5 $61.67 

Four  tons  pea  coal  for  blower,  at  $3.50 14.00 

Sand  and  clay 2.45 

Oil,  lights,  etc 4.40 

Wear  and  repairs  on  slag  and  matte-pots 3 . 85 

Wear  and  repairs  on  other  tools 1.12 

Daily  slight  repairs  on  furnace 2.60 

Proportion  of  radical  repairs  at  close  of  campaign  (found  by 

experience  to  be  3  cents  a  ton) 2.85 

Wear  on  belting,  blower,  etc 1 .25 

Engine  and  boiler 1 . 45 

Proportion  of  cost  of  blowing  in  and  out .72 

Sinking  fund 1 . 95 

Miscellaneous 6.50 

Labor  (per  twenty-four  hours) : 

Six  men  below  at  furnace 10.00 

Four  feeders 8. 00 

Six  wheelers 9.00 

Two  metal  men 4.00 

Two  laborers 3.00 

One  dump  man 2.00 

Two  foremen 5.00 

One  engineer 2.50 

Blacksmith  work 2 . 10 

Laboratory  work 2.00 

Superintendence 4.00 

Total $156.41 

Or  a  cost  per  ton  of $1 .64£ 

Adding  8  per  cent,  for  resmeltiug  slag  and  flue-dust,  gives 

total  cost  per  ton $1 .78 


CHAPTER  XL 

GENERAL  REMARKS   ON  BLAST-FURNACE    SMELTING. 

THE  capacity  of  a  blast-furnace  is  dependent  upon  many 
varying  causes,  and  is  to  a  considerable  extent  independent  of 
shape  or  size,  though  its  tuyere  area  is,  of  course,  the  most  im- 
portant factor  in  determining  the  amount  of  material  that  can 
be  passed  through  it. 

Next  to  the  fusibility  of  the  charge,  the  pressure  and  vol- 
ume of  the  blast  have  the  principal  influence  in  determining 
this  point,  assuming  always  that  the  fuel  used  is  of  sufficient 
strength  and  density  to  permit  the  full  pressure  of  wind  that 
may  be  found  most  advantageous. 

Nothing  can  be  more  striking  than  the  change  in  the  rate 
of  smelting  of  a  large  cupola-furnace  as  the  wind  pressure  is 
diminished  or  increased. 

The  author  has  taken  occasion  during  the  smelting  of  a 
fusible  charge,  and  with  the  furnace  in  perfect  condition,  to 
ascertain  the  difference  of  capacity  effected  by  changes  in  the 
strength  of  the  blast. 

As  the  influence  of  the  change  is  almost  instantaneous,  it 
is  easy  to  arrive  at  such  figures  with  considerable  accuracy, 
measuring  the  capacity  by  noting  the  number  of  pots  of  slag 
produced  during  periods  of  an  hour  each,  and  with  varying 
wind  pressure. 

The  following  table  shows  the  result  of  these  experiments 
in  a  compact  form,  repeated  sufficiently  often  under  varying 
conditions  to  establish  their  comparative  accuracy. 

It  should  be  mentioned  that,  in  order  to  insure  the  accuracy 
of  each  observation  independently  of  the  condition  of  the  fur- 
nace previous  to  the  experiment,  which  might  have  been  influ- 
enced by  the  preceding  test,  nearly  all  the  trials  were  made  at 
different  times,  but  with  the  furnace  as  nearly  at  its  normal 
state  as  possible,  and  running  under  its  ordinary  pressure  of 
blast — about  10  ounces  per  square  inch  : 


GENERAL   REMARKS  ON  BLAST-FURNACE  SMELTING.      247 


No. 
of 

test. 

Blast   pres- 
sure moz. 
per  sq.  in. 

Production  in 
tons  per  24 
hours. 

Assay    of    slag 
in  copper    at 
close. 

Condition  of  furnace  at  close  of 
experiment. 

1.. 
2.. 

1 

wt 

21 

0-27 
0-35 

Very  hot.    All  tuyeres  bright. 
Very  hot.    All  tuyeres  bright. 

3.. 
4-. 
5-. 
6-. 

2 
3 
4 
6 

81* 

44 

64 

86* 

0'30 
0-31 
0-31 
0-51 

Very  hot.    All  tuyeres  bright. 
Slag  hot  and  smoking.    Tuyeres  bright. 
Slag  hot  and  smoking.    Tuyeres  bright. 
Slag  hot  and  smoking.    Tuyeres  bright. 

7-- 

8 

87M 

0-40 

Slag  still  hot,  but  not  quite  so  strikingly 

8-. 

9 

91 

0-42 

so    as   with   lower   pressure.     Tuyeres 

*9.. 

10 

MX 

0-42 

satisfactory,  but  beginning  to  form  noses. 

10.. 

12 

113 

•  •  •  - 

11.. 

13 

111 

Less  hot.    Decided  noses. 

12.. 

14 

116 

0-66 

Much  cooler.    All  tuyeres  require  opening. 

These  tests,  although  not  entirely  uniform  in  every  respect, 
are  still  quite  regular,  and  agree  closely  with  many  previous 
observations. 

With  a  light  blast,  the  capacity  falls  rapidly,  though  the 
temperature  rises,  and  the  reducing  action  becomes  more 
powerful,  as  evinced  by  the  reduction  of  the  oxidized  copper 
in  the  slag,  and  the  almost  invariable  appearance  of  small 
masses  of  metallic  iron  in  the  fore-hearth. 

"With  the  highest  available  blast,  14  ounces  per  square  inch 
the  production  still  increases,  though  only  slightly  above  the 
normal  capacity,  bat  it  is  evident  more  wind  is  introduced  than 
can  be  consumed  by  the  fuel ;  a  lowering  of  temperature  oc- 
curs, as  distinctly  shown  by  the  appearance  of  the  slag ;  the 
reducing  action  is  less  powerful,  as  seen  by  the  slag  assays  ;  and 
thick,  hard  noses  are  formed  about  each  wind  stream,  which 
would  soon  obstruct  the  blast,  and  probably  cause  a  general 
chilling  of  the  furnace. 

Thinking  that  some  of  these  evils  might  be  attributed  to 
the  volume  rather  than  the  pressure  of  the  blast,  the  tuyere 
openings  were  decreased  from  5J  to  3£  inches  in  diameter,  re- 
ducing the  capacity  of  the  furnace  about  10  per  cent.,  but  other- 
wise effecting  no  visible  alteration  in  the  phenomena  described. 

Judging  from  this  series  of  tests,  as  well  as  from  numerous 
former  trials,  when  smelting  both  lead  and  copper  ores  of 
many  different  varieties  in  cupolas  of  various  sizes  and  under 
very  varying  conditions,  it  seems  advisable  to  limit  the  blast 
pressure  to  the  point  just  indicated.  In  no  single  instance  has 
anything  more  than  a  temporary  increase  of  capacity  accom- 


*  Normal  pressure  and  slag  assay. 


248     MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

panied  a  blast  pressure  above  12  ounces  per  square  inch,  and 
the  rapid  cooling  of  the  furnace  and  formation  of  heavy  and 
solid  noses  have  soon  brought  the  experiment  to  a  termination. 

It  seems,  therefore,  that  a  pressure  of  from  8  to  12  ounces, 
with  a  tuyere  diameter  of  from  4  to  5J  inches,  is  best  suited 
to  the  ordinary  conditions  of  copper  smelting. 

The  employment  of  soft-wood  charcoal  or  other  fragile  fuel 
may  make  it  necessary  to  diminish  even  this  light  pressure, 
while  anthracite  may  demand  a  more  powerful  blast  for  its 
most  economical  use.  Information  is  wanting  regarding  the 
use  of  anthracite,  but  it  is  doubtful  whether  any  advantage 
would  be  gained  by  its  employment,  its  powerful  reducing 
qualities  causing  an  almost  certain  formation  of  sows. 

Of  the  employment  of  a  heated  blast  for  copper  smelting, 
the  author  must  plead  almost  complete  ignorance.  The  few 
details  that  he  can  gather  on  this  subject  indicate  that  no 
advantages  commensurate  with  the  cost  of  plant  have  been 
obtained  by  its  adoption,  and  the  tendency  of  a  hot  blast  to 
increase  both  temperature  and  reducing  action  is  obvious. 

The  common  claim  urged  by  inventors  and  manufacturers 
of  smelting-furnaces  is,  that  their  apparatus  is  capable  of  gen- 
erating a  temperature  much  higher  than  ordinary  furnaces. 

This  shows  an  entirely  mistaken  notion  of  the  process  of 
smelting,  where  our  constant  endeavor  is,  to  prevent  the  tem- 
perature rising  much  above  the  point  necessary  for  the  fusion 
of  the  earthy  constituents  into  a  liquid  and  homogeneous  slag. 

The  method  of  charging  is  pretty  nearly  universal,  and 
differs  radically  from  the  old  practice,  where  the  establishment 
and  preservation  of  a  nose  seemed  to  be  the  chief  aim  and  end 
of  the  smelter' s  labors. 

Both  ore  and  fuel  are  now  pretty  generaUy  spread  in  hori- 
zontal layers  over  the  whole  area  of  the  furnace,  instead  of 
throwing  the  coke  toward  the  center,  while  the  charge  was 
carefully  placed  against  the  walls. 

The  introduction  of  water-jacketed  cupolas  and  the  very 
general  adoption  of  the  conical  shape,  whereby  the  gases  escape 
with  less  velocity,  and  the  ore  is  forced  to  descend  in  the  neigh- 
borhood of  the  walls,  have  doubtless  initiated  this  method  of 
charging,  which  has  been  followed  with  advantage  by  those 


GENERAL  REMARKS   ON  BLAST-FURNACE  SMELTING.      249 

who  prefer  the  brick  furnace,  and  still  adhere  to  vertical  walls. 
This  mode  of  feeding,  however,  should  by  no  means  be 
blindly  adhered  to,  as  nothing  exerts  a  more  powerful  influence 
upon  the  running  of  the  furnace  or  has  a  more  important  effect 
in  keeping  it  in  normal  condition  than  skillful  and  judicious 
feeding. 

In  the  brick  furnace  especially,  the  position  of  feeder  is  one 
of  vital  importance,  and  the  experienced  furnace  foreman  will 
spend  a  large  proportion  of  his  time  on  the  charging  platform. 

This  matter  has  been  discussed  and  exemplified  in  the  sec- 
tion on  large  brick  furnaces,  and  is  worthy  of  the  most  careful 
study  and  attention. 

The  absolute  size  of  the  charge  to  be  used  must  vary  accord- 
ing to  local  conditions. 

The  most  important  of  these  are,  the  area  and  height  of 
furnace ;  mechanical  condition  of  ore  ;  nature  of  fuel ;  and 
extent  of  reducing  action  desired. 

Large  and  high  furnaces  naturally  require  heavier  charges 
of  ore  and  fuel ;  a  charge  made  up  almost  entirely  of  coarse 
material  may  safely  be  fed  in  thicker  layers  than  if  composed 
principally  of  fine  dirt,  which  opposes  a  powerful  obstacle  to 
the  passage  of  the  blast ;  a  heavy,  compact  coke  will  bear  a 
much  weightier  charge  than  light,  fragile  fuel,  like  soft-wood 
charcoal ;  and  a  more  thorough  mixing  of  ore  and  fuel,  as 
effected  by  using  small  charges,  will  undoubtedly  bring  about 
a  more  powerful  reducing  effect  than  when  the  different  strata 
are  of  sufficient  depth  to  retain  their  relative  position  to  a  con- 
siderable depth. 

While  very  numerous  exceptions  exist,  the  author  prefers, 
in  general,  large  charges  to  small  ones,  having  found,  as  a  rule, 
that  the  furnace  runs  more  smoothly  and  regularly,  and  also 
that  a  slight  saving  in  fuel  is  effected. 

This  observation  will  no  doubt  be  challenged  by  many 
competent  metallurgists,  but  is  the  result  of  too  long  experience 
to  be  disproved  without  actual  trial. 

In  only  one  instance  has  the  writer  attempted  to  determine 
this  point  by  actual  experiment ;  but  in  the  case  referred  to, 
the  conditions  of  the  trial  were  particularly  favorable  for  a  fair 
and  impartial  comparison. 


250     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

The  furnace  was  a  42-inch  water-jacket,  smelting  a  mixture 
of  reverberatorj  copper  slag  and  fine  unroasted  pyrites,  with 
gas  coke  as  a  fuel.  The  foreman,  who  was  a  most  skillful 
smelter,  was  directed  during  the  entire  experiment  to  give  his 
attention  to  the  consumption  of  fuel,  using  no  more  than  was 
necessary  to  attain  the  best  possible  results.  The  change  in 
the  size  of  the  charge  was  made  without  directing  his  attention 
particularly  to  it.  He  was  thus  left  to  discover  any  necessity 
for  a  change  in  the  weight  of  fuel. 

The  experiment  was  begun  with  large  charges — 1,480 
pounds  of  mixture — the  relation  of  the  fuel  to  the  same  being 
as  1  to  9-3.  This  was  maintained  for  72  hours,  the  furnace 
remaining  in  excellent  condition,  and  averaging  57  tons  per 
twenty-four  hours. 

The  charge  was  then  reduced  to  740  pounds,  just  one  half 
of  the  original  amount,  and  twenty-four  hours  were  allowed  to 
elapse,  to  permit  matters  to  find  their  normal  level  under  the 
new  conditions. 

Within  six  hours  of  the  substitution  of  the  smaller  charge, 
black  noses  began  to  form  on  the  tuyeres,  and  the  rate  of  smelt- 
ing became  decidedly  slower.  Several  empty  charges — that  is, 
fuel  without  ore — were  given  at  intervals  ;  but  it  became  evi- 
dent, from  increasing  irregularities,  that  the  furnace  was  grow- 
ing cold.  A  slight  addition  was  made  to  the  fuel  charge,  and 
after  a  considerable  number  of  trials,  the  normal  ratio  of  fuel 
to  ore  for  the  new  conditions  was  established,  and  the  steady 
run  resumed.  A  three  days'  average  was  taken,  as  in  the 
former  case,  and  showed  the  best  possible  ratio  between  charge 
and  fuel  to  be  as  8'6  to  1. 

The  charge  was  again  halved,  being  now  reduced  to  370 
pounds,  and  the  last-named  proportion  of  fuel  maintained 
until  circumstances  compelled  a  change. 

In  brief,  another  three  days'  observation  showed  a  further 
reduction  in  the  ratio  of  ore  to  fuel — 7'82  to  1  being  the  best 
attainable  results.  It  is  also  interesting  to  note  that,  although 
great  pains  were  taken  to  secure  the  same  conditions  in  every 
particular  during  the  entire  course  of  the  experiment,  the 
matte  decreased  in  tenor  with  the  decrease  in  the  weight  of 
the  charge — the  average  assay  reports  for  the  three  periods  of 


GENERAL  REMARKS   ON  BLAST-FURNACE  SMELTING.       251 

three  days  each,  beginning  with  the  heaviest  charge,  being  re- 
spectively 46*4,  44'5,  and  42*1  per  cent. — the  amount  of  the 
same  increasing  with  its  poorness  in  a  very  nearly  correspond- 
ing degree.  The  slag  also  (although  this  may  have  been  a  coin- 
cidence) showed  lower  proportions  of  copper,  assaying  for  the 
three  periods  respectively  0*61, 0*47,  and  0*41,  which  is  a  greater 
difference  than  can  be  accounted  for  by  the  lower  grade  of  the 
matte,  and  which  in  all  probability,  in  common  with  the  latter 
material,  depended  upon  the  more  powerful  reducing  effect,  due 
to  the  use  of  thinner  charges,  and  a  consequently  more  perfect 
mingling  of  ore  and  fuel.  The  capacity  fell  from  57  tons,  in 
the  first  instance,  to  51  in  the  second,  and  down  to  41'5  in  the 
third. 

The  experience  at  several  Arizona  furnaces  contradicts  the 
above  results,  quite  small  charges  having  been  found  to  an- 
swer best,  although  this  may  be  due  to  the  fact  that  much  of 
the  ore  there  is  fine,  while  a  powerful  reducing  action  is  neces- 
sary to  produce  a  clean  slag. 

A  proper  charge  for  a  36-inch  furnace  is  from  500  to  800 
pounds ;  while  a  42-inch  shaft  should  receive  from  1,200  to 
1,600,  and  a  48-inch  furnace,  1,800  pounds  or  more.  The 
large  elliptical  slag-furnaces  at  the  Lake  Kefining- Works  are 
charged  with  about  2,600  pounds  of  ore  and  flux,  experience 
having  shown  the  advantage  of  deep  layers  in  the  furnace 
shaft. 

As  may  be  imagined,  the  large  Orford  furnaces  take  still 
heavier  charges,  from  3,000  to  4,000  pounds  being  the  ordi- 
nary standard. 

The  shape  of  the  furnace  is  largely  a  matter  of  individual 
preference,  as  may  be  seen  by  observing  the  almost  equal  num- 
ber of  skilled  advocates  for  the  round,  rectangular,  and  ellipti- 
cal form. 

Beyond  a  certain  limit,  however,  the  rectangular  form  alone 
is  used,  owing  to  the  feeble  penetration  of  the  light  blast  used 
in  copper  smelting. 

Experiments  made  by  Herreshoff  and  other  metallurgists, 
including  the  author,  seem  to  indicate  a  radius  of  28  inches  as 
about  the  extreme  practicable  limit  for  a  10-ounce  blast.  In  a 
larger  furnace,  while  the  writer  has  never  seen  any  evidence  of 


252     MODERN  AMERICAN  METHODS  OF  COPPER  SMELTING. 


an  untouched  central  core,  beyond  the  penetration  of  the  blast, 
the  capacity  increases  very  slowly,  if  at  all  ;  while  the  same 
area,  when  changed  into  a  rectangular  form,  gives  proportion- 
ately greater  results. 

If  the  charge  contains  over  50  per  cent,  of  fine  ore,  the 
figures  given  above  should  be  considerably  reduced. 

"While  the  effects  of  a  flaming  throat  are  not  so  obviously 
detrimental  in  copper  smelting  as  in  the  fusion  of  the  more 
volatile  metals,  it  still  is  found  by  experience  that  such  a  con- 


FROUT 


BLAST-PIPE  FOR  ORFORD  FURNACE 


dition  of  affairs  is  incompatible  with  the  best  work,  being  in- 
variably indicative  of  a  faulty  condition  of  the  process. 

With  an  open  charge  and  long-continued  high  pressure  of 
blast,  it  is  almost  impossible  to  prevent  the  heat  from  eventu- 
ally rising,  until  the  chimney  and  walls  above  the  charging-door 
become  so  hot  as  to  ignite  the  escaping  gases  instantaneously. 

The  ore  near  the  top  of  the  charge  soon  sinters  together  ; 
the  fuel  is  largely  consumed  before  it  reaches  the  zone  of 
fusion ;  the  softened  lumps  of  ore  stick  to  the  side  walls,  form- 


GENERAL  REMARKS  ON  BLAST-FURNACE  SMELTING.       253 

ing  bulky  accretions,  and  the  way  is  paved  for  the  successive 
steps  of  "  burning  out,"  reduction  of  metallic  iron,  and  "  freez- 
ing up,"  already  so  frequently  alluded  to. 

While  it  is  sometimes  impossible  to  prevent  the  early  stage 
of  this  condition  of  affairs,  when  pushing  the  furnace  to  its  full 
capacity  with  a  heavy  blast,  the  end  results  should  be  borne  in 
mind  and  the  remedy  applied  in  time. 

This  consists  simply  in  letting  the  charge  sink — under  a 
light  blast — until  the  shaft  is  empty  for  a  distance  of  three  or 
four  feet  below  the  charging-door.  One  or  more  charges  of 
fusible  slag  are  then  given,  and  the  furnace  rapidly  filled  full 
with  its  normal  burden.  In  this  way,  the  overheated  walls  are 
cooled,  the  surface  of  the  charge  regains  its  normal  tempera- 
ture, and  the  furnace  under  a  few  hours  of  light  blast  is  again 
ready  for  a  period  of  hard  driving. 

In  obstinate  cases,  the  cooling  of  the  throat  with  a  spray  of 
water  is  quite  admissible  and  often  of  great  benefit. 

The  question  of  the  characteristics  and  comparative  value 
of  the  ordinary  fuels  used  in  blast-furnace  work  has  been  dis- 
cussed so  exhaustively  in  most  of  the  standard  works  on 
metallurgy  as  to  render  it  useless  to  undertake  any  such  task 
in  a  treatise  like  the  present,  devoted  to  a  certain  stated  pur- 
pose. 

The  same  may  be  said  of  fire-brick  and  other  refractory  ma- 
terials, our  own  domestic  brick  being  quite  equal  to  any  of  for- 
eign make  for  all  purposes  connected  with  blast-furnace  smelt- 
ing. It  is  hardly  necessary  to  say  that,  among  the  numerous 
competing  varieties  of  fire-brick,  only  those  should  be  selected 
which  long  and  thorough  trial  has  shown  to  be  suited  to  the 
purpose ;  the  first  cost  should  have  but  slight  weight  in  the 
choice. 

The  manipulation  of  the  products  of  fusion  becomes  a 
question  of  considerable  importance  in  a  country  where  wages 
are  high,  and  where  the  large  scale  on  which  most  enterprises 
are  conducted  renders  the  mechanical  details  of  the  process  so 
much  more  prominent  than  in  the  European  works  from  which 
we  drew  our  first  patterns. 

The  transportation  of  the  slag  from  a  furnace  smelting  five 
tons  an  hour,  and  where  the  edge  of  the  dump  advances  at  a 


254      MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

rate  of  several  feet  a  week,  soon  becomes  a  matter  of  consid- 
erable expense. 

Aside  from  the  removal  by  a  current  of  water,  mentioned 
in  an  earlier  chapter,  no  advance  has  been  made  on  the  two- 
wheeled  slag-pot,  although  so  much  difficulty  has  at  times 
been  experienced  in  removing  the  slag  in  this  manner  with 
sufficient  rapidity  as  to  necessitate  the  addition  of  a  second 
fore-hearth  and  slag-run  to  the  furnace,  on  the  opposite  side 
from  the  original  opening. 

Little  need  be  said  regarding  the  slag-buggies  as  furnished 


SLAG- POT 

U9KO  BY 

CRFORD  CQPPEfl  AND  SULPHUR  CO, 
BER6ENPORTN.J, 

SCALL-f  TO  FOOT; 


by  the  manufacturers  of  metallurgical  appliances,  except  to 
urge  the  necessity  of  extreme  lightness  combined  with  strength. 
The  attachment  between  pot  and  axle  is  rarely  sufficiently 
strong,  and  the  axle  itself  should  be  chilled  or  case-hardened  to 
prevent  its  rapid  destruction  where  the  wheel  takes  its  bear- 
ing. The  accompanying  cut  shows  the  form  of  slag-buggy 
adopted  by  the  Orford  Company,  and  is  the  best  and  strong- 
est pattern  known  to  the  author. 

The  ordinary  complement  of  slag-pots  to  a  50-ton  furnace 
is  10,  which  number  should  be  doubled  if  it  is  expected  to  allow 
the  slag  to  cool  before  dumping,  as  should  always  be  done  if 


GENERAL  REMARKS   ON  BLAST-FURNACE   SMELTING.       255 

possible,  in  order  that  the  bottom  of  every  potful  may  be  ex- 
amined for  shots  of  matte. 

Great  care  should  be  taken  to  maintain  the  dump  perfectly 
smooth,  which  may  be  easily  effected  by  pouring  pots  of  liquid 
slag  over  its  entire  surface.  The  sole  duty  of  one  experienced 
workman  should  be  to  examine  the  slag  and  keep  the  dump  in 
order,  by  which  means  a  control  of  the  smelting  is  maintained 
and  the  labor  of  the  pot-runners  greatly  lessened. 

As  slag-dumps  are  not  infrequently  situated  on  the  margin 
of  a  river  or  lake,  the  danger  of  dumping  entire  pots  of  slag 
into  water,  when  they  are  only  partially  cooled,  should  always 
be  impressed  upon  the  workmen.  Terrific  explosions  some- 
times result  from  the  penetration  of  water  to  the  liquid  center 
of  a  cake  of  slag  that  appears  quite  solid  on  the  outside. 

The  writer  has  seen,  from  this  cause,  several  men  badly  in- 
jured ;  the  iron  roof  and  siding  partially  stripped  from  a  build- 
ing 200  feet  distant,  and  an  entire  town  a  mile  distant  alarmed 
by  the  explosion  of  a  cake  of  slag. 

BLOWERS  AND  ACCESSORY  BLAST  APPARATUS. 

All  apparatus  employed  for  the  production  of  a  blast  may 
be  divided  into  two  classes : 

I.  Those  producing  a  positive  blast,  and  which,  if  obstruct- 
ed, must  result  in  the  bursting  of  some  part  of  the  apparatus 
or  the  stopping  of  the  blower. 

II.  Centrifugal  fan-blowers,  which,  even  if  obstructed,  con- 
tinue  revolving,    consuming    much    less    power   than   when 
engaged  in  actual  work,  as  the  air  is  simply  beaten  by  the 
vanes,  and  revolved  in  the  machine  itself,  without  passing  out 
of  the  pipe. 

This  distinction  is  not  always  clearly  appreciated,  and 
serious  mistakes  in  the  construction  of  the  plant  sometimes 
arise  from  a  misunderstanding  of  the  properties  of  the 
machine  which  is  to  furnish  the  blast. 

Such  errors  can  always  be  avoided  by  application  to  a  rep- 
utable manufacturer  of  blowing  apparatus,  as  the  subject  is 
one  to  which  much  attention  has  been  paid  by  these  parties, 
who  are  for  the  most  part  quite  capable  of  planning  and  erect- 


256      MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

ing  a  suitable  blowing  plant  upon  a  full  understanding  of  the 
requirements  of  the  case. 

Owing  to  the  light  blast  used  by  all  copper  smelters  in  the 
United  States,  the  high-priced  cylinder  blowers,  as  required 
in  iron  smelting  plants,  are  seldom,  if  ever,  adopted. 

The  blowers  in  almost  universal  use  are  frequently  styled 
"fan-blowers"  in  general;  but  this  is  a  misnomer;  for  al- 
though it  is  true  that  both  types  of  blower  in  common  use 
resemble  a  fan  in  appearance,  the  results  obtained  are  widely 
different ;  one  class  belonging  to  the  first  section,  or  "  positive 
pressure  blowers,"  while  the  other  is  truly  a  "  centrifugal  fan- 
blower,"  and  belongs  under  the  second  heading. 

To  the  positive  pressure  blowers  belong  the  "Root," 
"  Baker,"  and  "  McKenzie  "  blowers,  all  of  which  are  too  well 
and  favorably  known  to  require  description  or  recommenda- 
tion. 

The  volume  of  air  delivered  by  one  of  these  machines  can 
be  calculated  with  great  accuracy,  while  the  pressure  simply 
depends  on  the  rapidity  of  revolution. 

From  the  nature  of  the  apparatus,  the  wind  is  delivered  in 
a  succession  of  rapid  but  distinct  impulses  and  puffs,  to  which 
peculiarity  the  adherents  of  the  apparatus  attach  a  great, 
although  somewhat  mysterious,  virtue,  while  its  rivals  bring 
forward  equally  convincing  proofs  of  its  damaging  effects  upon 
the  smelting  process. 

According  to  the  author's  experience  with  the  principal 
makes  of  domestic  blast  machinery,  these  puffs  have  neither  a 
damaging  nor  beneficial  effect ;  an  unbroken  stream  of  wind  of 
equal  volume  and  pressure  producing  exactly  similar  results. 

From  the  nature  of  the  apparatus,  more  power  must  be 
required  to  drive  its  closely  fitting  parts  than  if  they  revolved 
freely  in  space,  while  the  cog  gearing  by  which  motion  is 
imparted  to  the  piston  in  most  instances  produces  its  disa- 
greeable sound  and  adds  to  the  number  of  parts  subject  to 
wear. 

But  the  workmanship  is  so  excellent,  and  the  various  parts 
in  the  modern  machines  of  this  type  are  so  admirably  fitted 
and  adjusted,  that  the  evils  just  mentioned  are  reduced  to  a 
minimum;  while  the  nature  of  the  blower  is  such  that  only  a 


GENERAL  REMARKS  ON  BLAST-FURNACE  SMELTING.       257 

comparatively  slow  motion  is  required  to  produce  the  desired 
effect. 

The  machines  of  the  second  class,  or  centrifugal  fan-blow- 
ers proper,  consist  merely  of  a  light  blast-wheel  revolving  in 
an  inclosure  of  much  greater  diameter,  and  so  shaped  that 
wind  enters  the  escape-pipe  largely  from  the  centrifugal  force 
acquired  by  the  enormous  velocity  imparted  to  it  by  the  fan. 

The  smaller  blowers  make  from  4,000  to  5,000  revolutions  a 
minute,  and  those  of  even  5  or  6  feet  in  diameter  are  speeded 
up  to  1,500  or  2,000. 

While  this  is  an  excellent  device  for  the  delivery  of  a  large 
volume  of  wind,  the  element  of  pressure  is  only  obtained  by  a 
great  waste  of  power,  the  speed  necessary  to  produce  a  given 
pressure  increasing  out  of  all  proportion  to  the  gain  in  that 
quality. 

The  admirable  workmanship  of  the  "  Sturtevant "  and  of 
other  kindred  fans,  and  the  skill  with  which  the  inherent 
defects  of  this  method  of  gaining  pressure  have  been  reduced 
to  a  minimum,  have  caused  the  adoption  of  this  form  of 
blower  in  many  establishments  where  a  considerable  pressure 
is  required. 

But  while  the  writer  fully  recognizes  its  usefulness  over  a 
very  wide  range,  its  fatal  defects  as  a  blower  for  smelting  pur- 
poses cannot  be  concealed. 

A  cupola,  for  instance,  filled  to  the  throat  with  fine  ore 
and  using  for  fuel  a  very  dense  variety  of  coke,  shows  evi- 
dences of  chilling,  while  the  tuyeres  become  capped  with  a 
tenacious  slag,  which  requires  a  forced  blast  to  keep  them 
open.  If  the  blast  is  derived  from  a  positive  blower,  it  rises 
to  the  occasion,  and  the  pressure  of  the  wind  keeps  pace  with 
the  growing  obstruction,  as  may  be  seen  by  observing  the 
gauge.  More  work  is  thrown  on  the  engine,  and  the  pressure 
rises  until  the  obstruction  is  cleared  away,  or  some  portion  of 
the  machinery  or  blast-pipe  is  overtaxed.  (A  safety-valve 
should  always  be  provided  with  positive  blowers.) 

The  result  is  quite  different  with  the  fan  ;  for  as  the  wind- 
stream  is  obstructed,  so  is  the  delivery  lessened,  until  finally, 
with  the  complete  closure  of  all  blast  openings,  the  work  of 
the  engine  drops  to  almost  nothing,  and  the  fan  revolves  at  its 
17 


258     MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

full  speed,  neither  receiving  nor  delivering  a  cubic  inch  of  blast. 
This  may  be  easily  verified  by  suddenly  shutting  the  main 
blast-gate  between  the  fan  and  the  furnace.  The  unaltered 
stand  of  the  manometer  and  the  sudden  decrease  of  the  labor 
performed  by  the  motive  power  will  sufficiently  convince  the 
most  skeptical. 

With  coarse  ore,  an  easily  fusible  charge,  and  large  tuyere 
openings,  the  lightness,  compactness,  and  low  first  cost  may 
speak  in  favor  of  the  fan-blower  for  cupola  work. 

The  Orford  Company  makes  use  of  the  fan  even  for  its 
enormous  furnaces,  but  expends  from  50  to  75  horse-power  in 
obtaining  a  blast  that,  according  to  both  theory  and  experience, 
could  be  produced  with  about  one-third  of  this  expenditure 
of  force  with  the  positive  blower.* 

Where  the  positive  blower  is  used,  it  is  an  excellent 
arrangement  to  have  engine  and  blower  combined,  thus  ren- 
dering the  blast  entirely  independent  of  the  remaining  plant. 

Owing  to  the  vastly  varied  practice  in  regard  to  the  size  of 
tuyeres  used,  and  consequently  in  the  volume  of  wind  required, 
it  is  difficult  to  give  accurate  figures  regarding  the  power 
required  for  a  furnace  of  any  given  size. 

Elaborate  tables,  showing  the  horse-power  required  under 
nearly  all  possible  conditions,  are  issued  by  the  blower  manu- 
facturers, and  are  in  many  cases  quite  correct,  as  controlled 
by  indicator  cards  taken  in  the  presence  of  the  writer. 

As  a  guide  for  possible  estimates,  it  may  be  assumed  that 
eight  horse-power  will  drive  a  positive  blower  suitable  for  a 
36-inch  furnace,  while  a  48-inch  cupola  will  require  from  12  to 
14  horse-power. 

The  speed  required  by  the  fan-blowers  is  so  great  as  to 
demand  some  attention  to  the  arrangement  of  pulleys  and 
shafting  to  obtain  the  same. 

Care  should  be  taken  to  use  the  largest  sized  pulleys  prac- 
ticable, both  for  driving  and  receiving,  and  all  abrupt  belting 
from  very  large  to  very  small  pulleys  will  always  give  trouble. 

A  much  neglected  portion  of  the  blowing-plant  is  the  pipe 

*  Experiments  by  Mr.  H.  M.  Howe  contradict  this  statement,  as  regards 
power  required,  but  the  author  is  not  willing  to  accept  their  results  in  defi- 
ance of  long  years  of  practical  observation. 


GENERAL   REMARKS   ON   BLAST-FURNACE  SMELTING.       259 

that  conveys   the  blast.     By  a  strict  observance  of  the  fol- 
lowing rules,  much  annoyance  may  be  avoided. 

Use  galvanized  iron,  No.  22  to  24.  For  any  length  of  pipe 
up  to  50  feet,  make  the  blast-pipe  20  per  cent,  larger  in  diam- 
eter than  the  outlet  of  the  blower.  For  from  100  feet  to  200 
feet,  30  per  cent,  larger,  and  if  the  distance  be  over  200  feet, 
make  the  entire  pipe  50  per  cent,  larger.  This  precaution  will 
diminish  friction  and  greatly  increase  the  effective  blast. 

If  branches  are  used,  remember  that,  on  account  of  friction, 
two  pipes  of  a  given  area  can  convey  only  about  three-quarters 
the  wind  of  a  single  pipe  of  their  combined  area. 

Make  easy  curves,  avoiding  all  angles. 

All  joints  should  be  riveted  and  soldered.  Remember  that 
the  slightest  leak  may  reduce  the  effectiveness  of  the  blast  to 
an  enormous  extent. 

Have  tight-fitting  blast-gates  in  the  main  pipe  and  at  each 
tuyere. 

Maintain  a  reliable  quicksilver  manometer  connected  with 
the  wind-box  surrounding  the  furnace,  and  accustom  your 
furnace-men  to  rely  upon  it  as  the  seaman  relies  upon  the 
barometer. 

Remember,  in  this  connection,  however,  that  with  a  positive 
blower,  a  high  stand  of  the  manometer  may  indicate  that  the 
tuyeres  are  obstructed  as  well  as  that  the  blower  is  working 
satisfactorily. 

A  heavy  boiler-iron  damper  should  always  be  fitted  in  the 
cupola  flue  or  down-take,  and  should  be  lowered  to  just  such  a 
point  that  the  fumes  escape  lazily,  but  without  issuing  from  the 
charging-door.  By  this  precaution,  a  diminution  of  90  per 
cent,  in  the  amount  of  flue-dust  may  be  effected — by  accurate 
and  long-continued  trial. 

MODERN  AND  ACCESSORY  BLAST-FURNACE  APPARATUS. 

"While  the  slag  from  nearly  all  American  copper  cupolas  is 
run  into  movable  pots  and  thus  conveyed  to  the  dump,  the 
more  valuable  product  is  handled  in  several  different  ways, 
according  to  its  richness  and  to  local  custom. 

Furnaces  containing  an  inner  crucible  or  an  exterior  fore- 
hearth,  in  which  the  metal  collects  in  considerable  quantities, 


260      MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

and  where  no  metallic  copper  is  produced,  are  usually  tapped 
into  sand-molds,  made  of  a  slightly  moistened  sandy  loam. 
With  proper  management,  this  method  is  economical  and  sat- 
isfactory, and  suited  to  almost  any  grade  of  metal  ;  but  to 
avoid  the  untidiness  resulting  from  the  presence  of  a  large 
quantity  of  sand  in  the  neighborhood  of  the  furnace,  as  well 
as  the  frequent  mixing  of  the  same  with  the  liquid  matte  from 
careless  manipulation,  a  series  of  heavy  cast-iron  molds, 
communicating  with  each  other  by  lateral  projecting  lips,  is 
sometimes  preferred.  It  is  necessary  to  warm  them  thoroughly 
just  before  tapping,  to  prevent  injury  from  the  enormous  tem- 
perature to  which  they  are  exposed. 

The  Western  water-jacket  furnaces  are  almost  invariably 
provided  with  two  iron  spouts — one  in  front,  for  slag;  the 
other,  at  the  back  or  side  of  the  furnace,  and  several  inches 
below  the  former,  for  metal. 

The  slag  is  tapped  into  pots  at  intervals  of  from  five  to 
fifteen  minutes,  by  piercing  a  clay  plug  with  a  light  pointed 
steel  bar,  while  the  metal  collects  until  the  space  between  the 
two  spouts  is  filled,  when  it  is  tapped  into  rectangular  iron 
molds,  with  tapering  sides  and  ends,  and  mounted  on  wheels. 
The  ordinary  weight  of  the  pigs  thus  produced  is  from  250  to 
400  pounds.  The  method  is  convenient  and  cleanly,  though  a 
considerable  expense  arises  from  the  rapid  destruction  of  the 
metal  molds. 

In  furnaces  provided  with  a  siphon-tap,  and  in  which  the 
molten  products  flow  continuously,  the  matte  is  usually  received 
into  ordinary  slag-pots,  and  allowed  to  stand  until  it  is  chilled 
sufficiently  to  be  dumped  on  to  the  floor  of  the  building.  This 
practice  not  only  requires  a  large  number  of  pots,  but  also 
leaves  the  matte  in  a  peculiarly  massive  and  unmanageable 
condition,  some  of  the  lower  grades  of  metal  produced  from 
basic  ores  being  almost  malleable  from  the  excess  of  iron 
present.  It  is  at  times  hardly  possible  to  break  them  with  a 
heavy  sledge,  and  their  subsequent  crushing  is  ruinous  to  the 
machinery  employed. 

On  this  account,  the  old  plan  of  pouring  the  liquid  matte  on 
to  a  cold  iron  plate  is  sometimes  adopted,  and  with  very  satis- 
factory results.  Heavy  plates  of  cast-iron  are  used,  30  by  55 


GENERAL  REMAEKS   ON  BLAST-FURNACE   SMELTING.       261 

inches,  and  from  2  to  3  inches  thick.  These  are  inclosed  by  a 
tapering  border,  some  3  inches  high ;  and  the  liquid  matte, 
when  poured  upon  them,  spreads  out  at  once  into  a  thin  sheet 
which  is  easily  broken  up  into  sizes  suitable  for  immediate 
stall  or  heap  roasting,  and  in  excellent  condition  for  pulveriza- 
tion. 

An  ingenious  improvement  in  connection  with  "  tapping  " 
has  been  introduced  into  the  Grant  S melting-Works,  and  other 
Colorado  establishments,  and  although  intended  for  furnaces 
smelting  the  precious  metals,  may  be  applied  also  to  copper 
furnaces  where  the  manner  of  tapping  is  such  as  to  call  for  it 

When  copper  or  lead  matte  containing  the  precious  metals 
is  tapped  into  an  iron  pot  or  basin,  a  considerable  quantity  of 
slag  gushes  out  at  the  close  of  the  operation.  This,  owing  to 
splashes  of  metal,  which  have  spattered  over  the  sides  of  the 
pot  to  a  considerable  height,  becomes  so  rich  in  silver  (and 
gold)  as  to  cause  too  great  a  loss  if  thrown  away,  while  it  may 
yet  be  so  poor  as  scarcely  to  repay  another  fusion.  To  obviate 
this  difficulty,  at  some  works,  the  tapping-pot  is  provided  with 
several  plugged  openings,  at  about  the  point  corresponding 
with  the  lower  surface  of  the  slag  which  floats  upon  the  metal. 
After  tapping,  it  is  allowed  to  cool  for  a  few  moments,  when 
the  lateral  plug  is  pierced,  and  the  supernatant  slag  flows  out 
in  a  liquid  state,  leaving,  however,  a  thin  crust  covering  the 
walls  of  the  pot,  the  cold  iron  having  rapidly  chilled  the  slag 
with  which  it  was  ,in  contact,  and  which  also  contains  all  the 
metal  that  was  splashed  against  the  basin  in  tapping.  In  this 
manner,  a  few  pounds  of  slag  are  obtained,  assaying  from  12  to 
15  ounces  of  silver  to  the  ton,  in  place  of  some  hundreds  of 
pounds  containing  only  4  or  5  ounces  of  the  precious  metal. 

MATTE    SMELTING   IN  BLAST-FURNACES. 

To  one  accustomed  to  the  smelting  of  copper  ores  in  blast- 
furnaces, the  fusion  of  roasted  matte  presents  no  difficulties,  as 
the  homogeneity  and  fusibility  of  the  material,  coupled  with 
the  absence  of  silica,  alumina,  and  most  other  refractory  sub- 
stances, relieve  the  operation  of  its  chief  difficulties. 

A  single  examination  of  a  proper  sample  of  the  calcined 
material  reveals  the  proportion  of  oxide  of  iron — and  other 


262     MODEKN  AMERICAN  METHODS   OF  COPPER  SMELTING. 


—  present,  and  determines  the  amount  of  siliceous  flux 
that  must  be  added  to  produce  a  proper  slag. 

As  the  slag  resulting  from  the  fusion  of  matte  almost  al- 
ways contains  enough  copper  to  demand  its  further  treatment 
—  owing  to  the  extreme  richness  of  the  product  —  it  is  usually 
advantageous  to  add  the  smallest  possible  proportion  of  sili- 
ceous flux  compatible  with  the  formation  of  a  reasonably  pure 
slag.  In  this  way,  a  slag  is  obtained  that  is  so  rich  in  iron  as 
to  be  of  great  value  as  a  basic  flux  in  the  smelting  of  siliceous 
ores.  No  material  generally  accessible  to  the  metallurgist  is 
more  fusible  or  more  useful  in  correcting  a  faulty  mixture  or  in 
clearing  out  a  choked  furnace  than  the  one  in  question. 

If  carbonate  or  oxide  ores  of  a  siliceous  nature  are  avail- 
able, the  entire  aspect  of  the  smelting  process  is  changed  for 
the  better,  as  they  can  be  used  as  a  flux  for  the  roasted  matte, 
while,  being  free  from  sulphur,  their  copper  contents  assist  in 
producing  a  concentrated  matte  of  higher  percentage  than 
would  otherwise  result. 

The  last-mentioned  benefit  is  so  great  that  it  is  usually  pro- 
fitable to  purchase  such  ores  even  at  a  price  so  high  as  to 
leave  no  margin  after  deducting  the  working  costs. 

Owing  to  the  great  distances  between  most  of  the  establish- 
ments engaged  in  smelting  sulphide  ores  and  the  mines  pro- 
ducing siliceous  oxidized  ores  in  any  considerable  amounts, 
but  few  instances  occur  of  such  a  happy  condition  of  affairs  ; 
and  therefore  in  most  cases,  gravel,  pebbles,  and  other  barren 
substances  are  used  as  a  flux  to  the  matte. 

When  forced  to  adopt  this  unfortunate  practice,  experience 
has  shown  that  more  economical  and  better  results  are  ob- 
tained by  the  employment  of  some  acid  compound  —  such  as 
clay  slate,  silicate  of  alumina  with  a  small  proportion  of  other 
bases,  etc.  —  than  by  using  pure  silica,  in  the  shape  of  quartz 
pebbles,  crushed  quartz,  sand,  rock,  etc. 

The  extreme  infusibility  of  the  latter  requires  a  much 
higher  temperature  for  its  combination  with  the  protoxide  of 
iron  than  do  the  less  refractory  substances  named.  A  pretty 
thorough  trial  of  almost  every  available  material  has  led  to  a 
preference  for  ordinary  mica-schist  or  clay  slate  ;  the  next  best 
substance  is  broken  common  red  brick,  the  form  of  the  latter 


GENERAL  REMARKS  ON  BLAST-FURNACE  SMELTING.       263 

rendering  them  superior  to  the  clay  from  which  they  are 
made. 

In  all  cases,  the  siliceous  flux  should  be  broken  to  the  size  of 
walnuts  before  use  ;  otherwise,  irregularities  in  running  may  be 
anticipated,  especially  in  small  furnaces.  Minerals  containing 
any  considerable  proportion  of  silicate  of  magnesia  should  be 
avoided. 

It  seems  hardly  necessary  to  mention  that  the  simple  fu- 
sion of  unroasted  matte  in  a  cupola  furnace  produces  practically 
no  result  except  a  change  of  form,  the  removal  of  sulphur  by 
sublimation  being  so  slight  as  to  cause  an  enrichment  of  only 
one  or  two  per  cent. 

Although  this  subject  has  been  already  briefly  discussed, 
there  exists  such  a  widespread  idea  among  non-professional  men 
that  a  mere  fusion  of  the  matte  is  sufficient  to  increase  its  value 
that  a  positive  statement  to  the  contrary,  accompanied  with 
some  experiments  which  were  executed  to  demonstrate  this  fact 
to  a  doubting  director  of  a  smelting  company  may  prove  of 
value  in  some  future  instance. 

Twenty-six  tons  of  carefully  sampled  unroasted  matte, 
broken  to  the  size  of  an  egg,  were  smelted  in  ten  hours  in  a 
cupola  furnace  with  a  wind  pressure  of  one  inch  mercury. 
Twenty  per  cent  of  ordinary  ore  slag  was  added,  to  protect  the 
metal. 

On  accurately  weighing  and  sampling  the  product  of  fusion, 
the  following  results  were  obtained  : 

Weight  of  matte  smelted 26  tons. 

Weight  of  slag  smelted 2  60  tons. 

Assay  of  matte  smelted 33*50  percent. 

Assay  of  slag:  smelted 0  37  per  cent. 

Weight  of  matte  produced 25  07  tons. 

Assay  of  matte  produced 34'70  per  cent. 

of  slag  produced. 0*32  per  cent. 


Showing  an  enrichment  of  only  1-2  per  cent.  The  amount  of 
copper  produced  differs  only  0*001  per  cent,  from  the  amount 
charged,  showing  a  remarkable  agreement  in  assays,  weights,  etc. 

Further  experiments  were  made  with  corresponding  results, 
although  with  more  variation  in  the  figures  obtained. 

Notwithstanding  the   fusibility  of    the    mixture,   fully  as 


261     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

much  fuel  is  required  in  smelting  roasted  matte  with  its  silice- 
ous flux  as  in  the  case  of  calcined  ore,  one  pound  of  good  coke 
being  required  for  from  7  to  9  pounds  of  charge.  This  may 
result  from  the  great  quantity  of  reducing  gases  required  to 
lower  the  sesquioxide  of  iron,  which  is  usually  largely  present 
in  roasted  matte,  to  a  protoxide,  as  well  as  to  the  greater  ten- 
dency of  metallic  copper  or  very  rich  matte  to  chill  in  the  bot- 
tom of  the  furnace,  which  must  be  counteracted  by  an  addi- 
tional quantity  of  fuel 

The  same  pattern  of  furnace  used  for  smelting  ore  is  also 
applied  to  the  concentrating-fusion  of  matte,  the  height  of 
American  copper  cupolas  seldom  being  so  great  as  to  unfit 
them  for  this  work. 

The  richness  of  the  product  depends  on  the  thoroughness 
of  the  calcination,  as  well  as  on  the  extent  of  the  reducing 
action  in  the  smelting  process. 

It  is  seldom  that  the  calcination  has  been  executed  so  thor- 
oughly as  to  yield  solely  metallic  copper  in  fusion.  A  vari- 
able quantity  of  rich  matte  accompanies  the  metal.  The 
grade  of  the  copper  may  be  also  unduly  reduced  by  metallic 
iron,  as  was  the  case  in  the  Houghton  slag  smelting,  where 
the  anthracite  used  as  fuel  causes  a  large  and  unwelcome 
adulteration  of  the  copper  product  with  iron. 

This  is,  however,  unusual  in  American  practice,  the  low- 
ness  of  the  furnaces  and  the  rapidity  of  the  process  combining 
to  produce  a  tolerably  pure  metal,  as  will  be  seen  from  the  fol- 
lowing partial  analyses  of  pig-copper  resulting  from  the  fusion 
of  roasted  matte  in  the  cupolas  : 

Ely  pig-copper  (by  Nolten)  : 

Iron 1-6 

Sulphur .-.     0'8 

Copper 97-2 

99-6 

Ely  pig-copper  (by  Peters.     Selling  sample  of 
200,000  pounds) : 

Iron 1-1 

Sulphur 0'7 

Copper 98'4 

100-3 


GENERAL  REMAEKS   ON  BLAST-FURNACE   SMELTING.       265 

Ore  Knob  pig-copper  (by  Griffith) : 

Iron 1-4 

Sulphur 1-1 

Copper 96'8 

99-3 

A  comparison  of  the  foregoing  determinations,  which  repre- 
sent the  average  condition  of  very  large  quantities  of  black 
copper  as  produced  in  this  country  from  the  fusion  of  roasted 
matte,  with  the  following  analysis  from  Percy  of  the  average 
black  copper  produced  at  Atvidaberg,  Sweden,  will  show  the 
advantages  resulting  from  a  more  rapid  execution  of  the  pro- 
cess and  other  improvements : 

Copper 94-39 

Iron 2-04 

Zinc 1-55 

Cobalt  and  nickel 0'63 

Tin 0-07 

Lead  and  eilver 0'30 

Sulphur 0'80 


99-78 

An  average  sample  of  pig-copper  from  the  Detroit  and 
Lake  Superior  Smelting  Company's  cupolas  at  Houghton  con- 
tained only  94  per  cent,  copper,  the  remainder  being  princi- 
pally sulphur  and  iron.  This  extreme  impurity,  from  such 
remarkably  clean  metallic  ores,  arises  from  the  sulphur  in  the 
anthracite  used  as  fuel,  and  the  excessively  powerful  reducing 
action,  especially  when  it  is  charged  in  the  ratio  of  about  one 
pound  to  each  four  pounds  of  material  smelted. 

The  presence  of  zinc,  cobalt,  nickel,  etc.,  in  Dr.  Percy's  sam- 
ple of  Swedish  copper  will  account  in  part  for  the  low  grade  of 
the  black  copper,  but  the  principal  reasons  for  the  difference  in 
quality  are  those  already  mentioned. 

Three  samples  of  black  copper  from  the  celebrated  Mans- 
feld  works  in  Prussia,  made  respectively  by  Berthier,  Hoff- 
man, and  Ebbinghaus,  contained  95'45,  89-13,  and  92'83  per 
cent,  of  copper ;  while  two  determinations  of  the  same  mate- 
rial from  the  Kiecheldorf  Smelting-Works,  in  Germany,  by 
Genth,  give  respectively  83'29  and  92*24  per  cent,  of  metal. 


266      MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

The  influence  exercised  on  the  succeeding  operations  by 
the  purity  of  this  product  is  very  great,  the  lower  grades  of 
black  copper  requiring  one  or  more  oxidizing  fusions  to  bring 
them  to  the  same  purity  as  that  already  possessed  by  the  im- 
mediate product  of  most  American  furnaces  used  for  the  pro- 
duction of  pig-copper. 

The  product  of  matte  concentration  in  blast-furnaces  dif- 
fers from  that  derived  from  the  same  process  when  executed 
in  reverberatories  in  not  being  homogeneous,  but  consisting 
usually  of  a  matte  of  medium  high  grade,  together  with  a  cer- 
tain proportion  of  metallic  copper,  where,  in  the  latter  case,  it 
would  consist  entirely  of  a  matte  of  very  high  grade.  This  is 
a  most  interesting  fact,  and  yet  awaits  a  satisfactory  explana- 
tion. 

The  large  brick  furnaces  already  described  are  also  used 
with  advantage  for  matte  concentration,  their  principal  draw- 
back being  the  inevitable  tying  up  of  a  large  quantity  of  metal 
in  the  bottom  of  the  cupola.  This  deposit  increases  according 
to  the  quantity  smelted,  and  even  in  a  well-constructed  furnace 
may  amount  to  20  tons  or  more.  This  drawback  will  doubt- 
less be  eventually  overcome,  but  for  the  present  prohibits  the 
employment  of  such  cupolas  for  the  purpose  indicated  for  any 
but  very  large  metallurgical  concerns,  which  can  afford  to  sub- 
mit to  the  locking  up  of  such  a  large  amount  of  metal  for  the 
sake  of  the  economical  advantages  belonging  to  this  type  of 
furnace. 

TREATMENT  OF   FINE  ORE  IN  BLAST-FURNACES. 

The  mechanical  condition  of  the  ore  to  be  smelted  in  blast- 
furnaces is  a  matter  of  scarcely  less  importance  than  its  chem- 
ical constitution. 

The  evils  resulting  from  an  undue  proportion  of  fines  are 
well  known. 

The  formation  of  an  immense  quantity  of  flue-dust  is  one  of 
the  least  of  these  evils,  as  provision  can  be  made  for  its  collec- 
tion and  reworking,  though  at  an  increased  cost ;  but  the  dif- 
ficulties resulting  from  the  choking  of  the  furnace,  and  the  sift- 
ing of  the  fine  ore  through  the  charge  until  it  pours  out  in  a 
stream  through  the  tuyere-openings,  scarcely  altered  by  its 


GENERAL  REMARKS   ON  BLAST-FURNACE  SMELTING.       267 

passage  through  the  furnace,  are  radical,  and  incompatible 
with  either  proper  or  economical  work. 

The  extent  of  this  evil  has  encouraged  the  invention  of  a 
great  variety  of  methods  for  its  removal,  most  of  them  relating 
to  a  consolidation  of  the  fine  material  into  lumps  of  a  suitable 
size. 

The  agglomeration  of  the  fine  ore  in  the  calcining-furnace 
has  been  suggested ;  but  the  great  expense  of  fuel  and  the 
heavy  losses  inseparable  from  a  method  that,  however  applica- 
ble to  such  an  easily  fused  substance  as  silicate  of  lead,  would 
be  entirely  impracticable  when  dealing  with  oxide  of  iron, 
render  it  unnecessary  to  discuss  this  practice. 

Assuming  that  the  only  feasible  remedy  consists  in  forming 
the  fine  ore  into  blocks,  the  experiments  executed  naturally 
fall  into  three  divisions  : 

1.  Bricking  by  the  aid  of  some  foreign  substance  that  has 
the  power  of  holding  the  ore  particles  together. 

2.  Bricking  by  pressure  alone. 

3.  A  combination  of  the  two  methods. 

The  materials  tried  by  the  writer  and  included  under  the 
first  heading  are :  Silicate  of  soda  (soluble  glass),  unslacked 
lime,  clay,  hydraulic  cement,  coal-tar  and  similar  substances, 
sulphate  of  iron. 

In  nearly  all  cases,  a  certain  degree  of  pressure  must  be 
used  to  form  or  mold  the  mixture  into  the  desired  shape  ;  this 
may  be  obtained  by  an  ordinary  brick-machine,  or  by  com- 
pressing with  the  hands,  using  a  mold  or  not.  In  No.  2,  press- 
ing alone  is  used.  A  thorough  mixture  of  the  ore  with  silicate 
of  soda  results  merely  in  the  coating  of  each  particle  with  a 
layer  of  soluble  glass,  and  in  nowise  facilitates  the  agglutination 
of  the  ore.  On  the  other  hand,  when  the  latter  is  already 
compressed  into  balls  or  blocks,  the  dipping  of  the  same  into 
a  strong  silicate  of  soda  solution  is  accompanied  with  great  ad- 
vantage, the  surface  becoming,  on  drying,  nearly  as  hard  as 
granite,  and  effectually  preventing  any  wastage  or  breakage  of 
the  lumps  by  handling.  (It  should  be  mentioned  that  the  cir- 
cular or  oval  shape  is  much  preferable  to  the  rectangular, 
owing  to  the  absence  of  fragile  edges  and  corners.) 

Of  course,  this  material  would  be  far  too  expensive  for  any 


268     MODERN  AMERICAN  METHODS   OF   COPPER   SMELTING. 

thing  but  the  richest  ore,  sufficient  water-glass  to  thoroughly 
coat  a  ton  of  balls  the  size  of  the  fist  costing,  at  Eastern 
wholesale  prices,  about  $3.25. 

No  substance  has  been  more  frequently  employed  for  the 
purpose  indicated  than  freshly  burned  lime,  which  should  be 
slacked  with  considerable  water,  and  the  resulting  milk  of  lime 
thoroughly  incorporated  with  the  ore,  until  the  entire  mass 
possesses  the  consistency  of  very  thick  mortar. 

This  is  usually  left  in.  a  heap  for  several  days,  and  then  fed 
into  the  furnace  in  the  shape  of  partially  dried  mud.  But 
much  better  results  are  obtained  by  forming  it  at  once  into 
balls  and  subjecting  it  either  to  the  hot  sun  or  to  a  gentle  arti- 
ficial heat  until  it  is  thoroughly  dry  and  hard.  The  resulting 
balls  are  somewhat  brittle  and  fragile,  and  demand  careful 
manipulation;  but  are  far  preferable  to  the  product  obtained  by 
leaving  it  in  a  heap,  and  exert  a  marked  effect  in  the  capacity 
and  condition  of  the  smelting-furnace. 

The  proportion  of  lime  necessary  to  effect  a  good  result 
varies  greatly,  according  to  the  physical  condition  of  the  ore, 
the  amount  of  sulphates  present  (which  form  a  strongly  cohe- 
sive cement  with  the  lime),  etc.,  but  is  usually  from  5  to  12 
per  cent. — less  than  5  per  cent,  seldom  producing  satisfactory 
bricks.  The  cost  of  mixing  alone  (lime  not  included)  is  from 
25  to  40  cents  a  ton  by  contract,  which  sum  must  be  doubled 
or  trebled  if  it  is  formed  into  bricks,  depending  upon  the  effect- 
iveness and  convenience  of  the  plant.  In  almost  all  cases,  the 
addition  of  lime  has  a  favorable  effect  upon  the  subsequent 
fusion.  It  is  probable  that,  when  the  water  is  removed  from 
the  lime  by  the  heat  of  the  furnace,  the  masses  again  crumble 
to  a  certain  extent,  but  not  until  they  have  already  undergone 
a  certain  preparation,  which  must  be  of  value,  to  judge  from 
the  results  obtained  in  actual  work.  This  method  was^carried 
out  extensively  at  the  "  Gap  "  nickel  mine,  Pennsylvania,  not 
only  the  roasted  fines, but  also  the  fine  raw  pyrites  being  thus 
treated,  previously  to  roasting  in  kilns  ;  the  results  of  the  lat- 
ter process  being  much  better  than  could  be  expected  from 
a  material  possessing  such  slight  cohesive  properties  as  fine 
granular  pyrites. 

The  Orford  Company  and  many  other  metallurgical  estab- 


GENERAL  EEMARKS   ON  BLAST-FURNACE  SMELTING.       269 

lishments  have  adopted  this  method  in  the  handling  of  finely 
pulverized,  calcined  matte,  although  in  most  cases  the  materials 
are  simply  mixed  into  a  thick  mortar,  and  charged  into  the  fur- 
nace after  lying  in  a  heap  for  a  few  days.  The  difficulties  and 
irregularities  in  the  running  of  the  cupola  that  would  certainly 
result  from  the  employment  of  an  excessive  proportion  of  such 
unfit  material  are  counteracted  to  a  considerable  extent  by  the 
addition  of  a  large  amount  of  slag,  which  serves  to  loosen  the 
charge  and  keep  everything  in  normal  condition. 

The  important  observation  has  also  been  made  by  Mr.  W. 
E.  C.  Eustis,  that  a  product  of  considerably  higher  grade  re- 
sults from  the  addition  of  some  5  per  cent,  of  lime  to  the  cal- 
cined matte.  The  substitution  of  limestone  fails  to  produce 
the  same  effect. 

In  consideration  of  the  advantages  already  enumerated, 
and  from  the  fact  of  its  cheapness,  general  availability,  and 
fluxing  qualities,  lime  may  be  regarded  as  the  most  useful  sub- 
stance yet  known  for  the  purpose  under  consideration,  and 
where  bricking  under  pressure,  with  subsequent  thorough  dry- 
ing, is  not  attempted. 

Clay  is  also  extensively  used  for  the  same  purpose,  and  if 
thoroughly  incorporated  with  the  fine  ore  and  allowed  to  dry 
for  a  reasonable  time  after  being  made  into  balls,  gives  a 
stronger  and  less  friable  product  than  lime.  The  quantity 
added  varies  from  2  to  5  per  cent. 

It  possesses  the  serious  disadvantage  of  adding  to  the  silice- 
ous contents  of  the  ore.  In  the  case  of  calcined  matte  or 
highly  basic  ores,  on  the  contrary,  it  forms  a  useful  flux.  The 
cheapest  variety  of  clay  that  possesses  the  required  plasticity 
should,  of  course,  be  selected. 

The  powerful  cohesive  qualities  of  ordinary  hydraulic 
cement  long  since  attracted  notice. 

Fortified  by  the  favorable  opinion  of  Prof.  J.  Eraser  Tor- 
ranee,  the  writer  has  employed  it  to  brick  jewelers'  sweeps, 
and  after  a  month's  trial,  is  quite  satisfied  with  the  results  ob- 
tained. 

He  finds  about  eight  per  cent,  of  cement  necessary  to  pro- 
duce balls  which,  after  a  week's  exposure  to  the  air,  will  bear 
moderate  handling,  and  give  good  results  in  the  furnace.  Of 


270      MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

course,  the  expense  of  this  method  forbids  its  use  for  ordinary 
substances. 

Where  coking  coal  is  available,  fine  ore  can  be  mixed  in 
large  proportions  with  the  coal  in  the  kiln  and  coked. 

Coal-tar  and  similar  substances  require  the  aid  of  quite 
powerful  compression  to  answer  the  required  purposes,  and 
have  not  been  found  practicable. 

A  solution  of  copperas — sulphate  of  iron — is  used  in  seve- 
ral of  the  European  works  to  agglomerate  fine  ore.  By  careful 
drying,  the  balls  made  with  this  substance  become  very  hard ; 
but  the  addition  of  sulphur  to  the  charge  (forming  a  percepti- 
ble increase  of  matte  in  cupola  work),  the  very  disagreeable 
effect  upon  the  skin  of  the  operatives,  and  other  minor  disad- 
vantages have  prevented  its  adoption. 

The  introduction  of  inexpensive  machines  for  the  manu- 
facture of  brick  from  almost  dry  clay,  and  capable  of  exerting 
an  immense  pressure,  has  opened  new  possibilities  to  the  me- 
tallurgist. Although,  doubtless,  such  exist,  the  author  can  find 
no  recorded  results  of  bricking  fine  ore  by  employing  pressure 
alone,  and  is  therefore  obliged  to  fall  back  upon  some  brief 
trials  made  under  his  directions  at  the  Parrot  Works,  Butte, 
Montana.  The  ore  used  consisted  of  pyrites  concentrates,  cal- 
cined so  thoroughly  as  to  contain  only  traces  of  soluble  sul- 
phates. The  brick-machine  used  produced  about  40  bricks  a 
minute,  weighing  5  pounds  each  dry,  and  exerted  a  pressure  of 
4  tons  per  square  inch.  Under  this  immense  force,  the  com- 
pressed ore  slabs  already  possessed  considerable  strength,  and 
could  be  backed  up  in  the  usual  manner. 

Unfortunately,  no  provision  had  been  made  for  drying  the 
brick  by  artificial  heat — a  most  essential  part  of  the  process. 
After  a  day's  exposure  to  the  air,  they  were  smelted  in  a  water- 
jacket  furnace,  breaking  up  to  a  considerable  extent  during 
transportation,  but  fusing  with  much  greater  rapidity  and  econ- 
omy than  when  in  a  fine  condition. 

A  few  that  were  dried  at  a  gentle  heat  for  six  hours  became 
so  hard  as  to  bear  any  reasonable  handling,  and  when  broken 
once  in  two,  were  admirably  adapted  for  blast-furnace  work. 
Kapid  drying  is  highly  injurious. 

The    writer    is    quite    convinced    of    the  value    of    this 


GENERAL   REMARKS   ON  BLAST-FURNACE   SMELTING.       271 

method,   and   considers  it   applicable   to   any   ordinary   ma- 
terial. 

The  essential  conditions,  after  obtaining  the  proper  pres- 
sure, are  a  gentle  and  sufficiently  prolonged  temperature,  and  a 
sufficient  space  to  dry  the  necessary  quantity.  A  series  of 
light  shelves  in  a  well-ventilated  building,  heated  by  steam- 
pipes,  would  seem  to  fulfill  these  requirements,  while  the  shape 
and  size  of  the  molds  could  be  adapted  to  the  purpose.  A 
round  or  oval  shape  is  best,  thus  escaping  the  wear  on  sharp 
corners  and  angles. 

The  cost  of  bricking  fine  ore  in  this  manner  in  Montana 
did  not  exceed  50  cents  a  ton ;  a  single  machine,  requiring  10 
horse-power  and  the  labor  of  8  men,  having  a  capacity  of  60 
tons  in  ten  hours. 

A  combination  of  the  two  foregoing  methods  was  effected 
by  incorporating  a  certain  proportion  of  lime  or  clay  with  the 
fine  ore,  before  submitting  it  to  the  immense  pressure  men- 
tioned. 

The  addition  of  from  2  to  4  per  cent,  of  either  of  these  sub- 
stances was  accompanied  with  an  increase  in  the  strength  and 
tenacity  of  the  product,  and  was  found  especially  useful  where 
the  process  of  drying  could  not  be  carried  out.  With  proper 
facilities  for  a  slow  but  perfect  desiccation,  no  such  addition  is 
necessary. 

In  place  of  clay,  fine  slimes  from  the  concentration  depart- 
ment or  other  sources  may  be  substituted,  and  their  metal  con- 
tents beneficiated  at  the  same  time.  This  practice  was  adopted 
by  Prof.  J.  A.  Church,  at  Tombstone,  Ariz.  An  ordinary  brick- 
machine  was  employed,  the  cohesive  property  of  the  slimes 
being  depended  on  to  bind  the  fine  ore  together. 

Fine  grinding  has  been  lately  proposed :  it  forms  a  pulp, 
which  becomes  tenacious  from  the  minuteness  of  its  particles. 
This  plan  is  widely  practiced  in  England  for  the  balling  of  the 
raw  Spanish  pyrites  fines,  preparatory  to  their  roasting  in 
kilns.  The  tenacity  generated  in  this  otherwise  granular  and 
uncohesive  material  by  a  mere  grinding  is  very  striking. 

Before  concluding  this  subject,  the  question  of  smelting 
fines  in  their  natural  condition  should  be  noticed. 

While  the  presence  in  a  cupola  smelting  charge  of  even  a 


272     MODERN  AMERICAN  METHODS   OP   COPPER  SMELTING. 

'moderate  percentage  of  fine  ore  is  accompanied  with  certain 
evils,  such  as  formation  of  flue-dust,  the  choking  of  the  furnace, 
irregularities  in  its  running,  descent  of  the  fine  ore  unprepared, 
until  it  even  pours  out  of  the  tuyeres,  scarcely  heated  above 
the  temperature  of  the  air,  etc.,  it  is  a  condition  that  is  almost 
invariably  met  with  to  a  certain  extent,  as  the  mere  transpor- 
tation of  ore  from  one  building  to  another  will  result  in  the 
formation  of  a  certain  amount  of  fines.  It  becomes  impor- 
tant, therefore,  to  determine  at  what  point  the  proportion 
of  fines  becomes  so  great  as  to  demand  measures  for  its 
relief. 

This  again  varies  greatly  with  the  quality  of  the  ore,  slag, 
and  metal,  the  power  of  the  blast,  size  of  furnace,  capacity  and 
efficiency  of  dust-chambers,  etc. 

Here,  as  in  most  other  instances,  no  experiments  have  been 
recorded  to  determine  this  important  point,  and  practice  varies 
with  the  prejudice  or  opinion  of  every  individual. 

The  following  experiments  were  made  on  ore  from  the 
Moose  mine,  in  Park  County,  Colorado,  in  1871,  and  though 
relating  to  the  treatment  of  silver  ore,  will  serve  the  present 
purpose  as  well  as  though  the  product  had  been  a  copper 
matte.  The  furnace  was  small — 2J  by  3  feet — and  smelting 
an  exceedingly  infusible  charge,  containing  over  40  per  cent, 
of  sulphate  of  baryta  and  much  silica. 

The  fuel  was  spruce  charcoal,  and  the  blast  very  weak, 
causing  an  extremely  slow  smelting  ;  but  as  the  conditions  re- 
mained the  same  throughout  all  the  experiments,  the  results 
possess  some  value. 

The  material  smelted  consisted  of  ores  from  the  Moose  and 
adjoining  mines,  from  which  all  that  would  pass  through  a  3- 
mesh  screen  had  been  separated,  to  be  submitted  to  a  calcina- 
tion, the  fine  ore  containing  a  much  greater  proportion  of  sul- 
phides than  the  coarse,  which  latter  was  smelted  raw. 

To  this  coarse  ore  was  added  a  certain  amount  of  carbon- 
ate of  lead  ores,  almost  free  from  fines  and  the  requisite  quan- 
tity of  heap-roasted  auriferous  iron  pyrites,  to  produce  a  fus- 
ible slag.  The  latter  material  contained,  after  roasting,  about 
25  per  cent,  of  fines  ;  and  the  mixture  as  prepared  for  the  fur- 
nace, and  without  the  addition  of  the  fine  calcined  silver  ore, 


GENERAL   REMARKS   ON  BLAST-FURNACE   SMELTING.       273 


carried  about  12  per  cent,  of  fines  that  would  pass  a  6-mesh 
screen. 

This  was  regarded  as  the  normal  charge,  to  which,  by  way 
of  experiment,  were  added  varying  proportions  of  the  roasted 
fines ;  all  other  conditions  remaining  as  nearly  identical  as 
was  practicable  thoughout  the  trials. 

Representing  the  quantity  of  this  normal  charge  that  would 
be  smelted  in  twenty-four  hours  by  100,  the  addition  of  fines 
produced  the  following  decrease  : 

10  per  cent,  fines  reduced  it  to 
20 


25 
30 
35 
40 
50 


.92 

.80^ 

.80 

.64 

.56 

.51 

.42 


Aside  from  the  decrease  in  capacity  accompanying  the  ad- 
dition of  fines,  serious  irregularities  in  the  running  of  the  fur- 
nace were  also  produced,  causing  an  increase  in  the  cost  of 
smelting  per  ton,  as  well  as  greatly  adding  to  the  labor  of  the 
men  and  to  the  proportion  of  silver  lost  in  the  slag. 

An  increase  in  the  area  of  the  furnace  greatly  heightens  its 
capacity  for  smelting  fine  ore  ;  and  the  results  obtained  in  this 
direction  by  the  use  of  the  large  Orford  furnace  are  very  strik- 
ing. 

The  presence  of  from  15  to  20  per  cent,  fines  seems  to  be 
no  drawback  at  all,  when  this  type  of  furnace  is  employed,  and 
even  from  50  to  60  per  cent,  of  the  charge  may  consist  of  this 
ordinarily  unwelcome  substance  without  seriously  affecting  the 
running  of  the  furnace,  although,  of  course,  its  capacity  will 
be  somewhat  reduced. 

After  smelting  a  charge  containing  a  very  high  proportion 
of  fines  for  from  24  to  36  hours,  it  will  usually  be  found  that 
cold,  unaltered  fines  appear  at  the  tuyeres.  This  results  from 
the  constant  agitation  of  the  charge  by  the  blast,  by  which  the 
ore  particles  are  sifted  down  through  the  interstices  between 
the  fuel  and  coarse  ore,  until  they  actually  reach  the  level  of 
the  hearth.  In  such  cases,  the  pipes  should  be  removed  and 
all  the  fine  ore  within  reach  raked  out  of  the  tuyere-holes, 
with  appropriate  tools. 
18 


274     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

All  feeding  from  above  should  now  cease  until  the  charge, 
under  a  light  blast,  has  sunk  nearly  to  the  tuyere  level,  when 
the  shaft  should  be  refilled  with  alternate  layers  of  fuel  and 
coarse  ore  in  the  usual  proportions,  after  which  the  use  of  fine 
ore  mav  be  resumed.  With  these  precautions,  a  very  large 
proportion  of  fine  ore  may  be  smelted  in  this  type  of  furnace, 
without  seriously  diminishing  its  capacity  or  producing  any 
irregularities  of  importance. 

The  attention  of  metallurgists  is  particularly  called  to  the 
ease  with  which  raw  fine  pyrites,  technically  called  "  green  fines," 
may  be  treated  in  this  furnace  with  the  fan-blast.  This  material 
often  accumulates  in  great  quantities  at  copper  mines,  as, 
owing  to  its  mechanical  condition,  it  cannot  be  roasted  in 
heaps,  while  pecuniary  considerations  may  forbid  the  erection 
of  an  extensive  calcining  plant  for  its  treatment.  Heretofore, 
when  of  low  grade  (from  1J  to  3£  per  cent.),  it  has  been  either 
thrown  aside  in  heaps,  or  allowed  to  harden  and  consolidate 
until  it  can  be  broken  out  in  lumps  and  added  to  the  roast- 
heaps.  By  this  practice  much  waste  occurs,  while  a  large 
amount  of  money  is  constantly  tied  up  in  this  material. 

After  experimenting,  Mr.  J.  L.  Thomson,  of  the  Orford 
Company,  found  that  a  charge  composed  of  this  material  and 
ferruginous  slag  from  the  concentration-fusion  of  copper  matte 
could  be  smelted  together  to  great  advantage  in  the  large  fur- 
nace ;  the  immense  volume  of  blast  employed  oxidizing  the 
raw  pyrites  to  a  considerable  extent,  and  producing  a  matte  of 
much  higher  grade  than  would  result  from  such  material  under 
ordinary  circumstances.  The  slag  from  matte  concentration 
always  carries  nearly  or  quite  enough  copper  (from  1  to  2  per 
cent.)  to  cover  the  cost  of  its  resmelting  where  fuel  is  cheap  ; 
while  the  large  percentage  of  protoxide  of  iron  that  it  carries 
neutralizes  the  silica  of  the  green  fines,  which  finds  no  base  in 
its  own  composition,  all  the  iron  that  it  contains  being  com- 
bined with  sulphur,  and  consequently  unavailable  for  slag  for- 
mation. 

Where  circumstances  do  not  favor  the  employment  of  the 
matte  slag,  this  may  be  replaced  by  heap-roasted  pyritic  ore  ; 
in  which  case,  of  course,  the  resulting  matte  will  be  somewhat 
richer.  - -.  :^t\; 


GENERAL  REMARKS   ON  BLAST-FURNACE  SMELTING.       275 

In  any  case,  the  slag  resulting  from  this  practice  is  distin- 
guished by  its  freedom  from  copper,  owing  to  the  overwhelm- 
ing amount  of  low-grade  matte  present,  which  cleanses  the  light 
siliceous  slag  to  an  unprecedented  degree.  Owing  to  the  large 
amount  of  unsatisfied  silica  in  the  green  ore,  the  slag  is  always 
exceedingly  acid,  containing  from  48  to  55  per  cent.  SiO2,  and 
often  being  so  sticky  and  thick  that  only  the  constant  and 
powerful  stream  of  intensely  hot,  low-grade  matte  keeps 
the  slag-run  open,  and  prevents  the  furnace  from  "  sticking 
up." 

The  oxidation  of  the  fine  sulphide  particles  by  the  air-blast 
carries  the  heat  to  the  surface  of  the  charge,  and  produces  to 
a  certain  extent  those  evils  inseparable  from  the  extension  of 
the  high  temperature  from  the  zone  of  fusion  to  the  upper 
layers  of  the  charge.  Owing  to  these  circumstances,  a  serious 
burning  of  the  brick  walls  often  takes  place,  which  circumstance, 
combined  with  the  cutting  down  of  the  furnace  bottom  from 
the  immense  quantity  of  fiery,  low-grade  metal,  favors  the 
practice  already  recommended  of  keeping  in  blast  only  during 
twelve  hours  out  of  the  twenty-four. 

The  siphon-tap  is  almost  indispensable  in  this  form  of 
smelting,  as  the  quantity  of  matte  produced  in  a  twenty-four 
hours'  run  often  amounts  to  25  or  30  tons. 

From  six  to  nine  months  has  been  the  ordinary  length  of 
campaign  for  these  large  brick  furnaces,  running  on  either  a 
siliceous  or  basic  slag,  at  the  expiration  of  which  time  a  week's 
repairs  will  again  fit  them  for  work. 

Not  feeling  at  liberty  to  give  the  results  obtained  in  the 
fusion  of  green  fines  at  the  Orford  Works,  where  this  practice 
originated,  the  author  is  forced  to  fall  back  upon  results  in  his 
own  practice,  where  the  total  quantities  treated,  though  much 
smaller,  still  aggregate  some  30,000  tons.  During  a  four  months' 
campaign,  in  which  a  mixture  of  green  fines  and  matte  slag 
were  treated  in  a  large  Orford  furnace,  the  average  daily 
(twenty-four  hours)  results  were  as  follows  : 

Weight  of  green  fines  smelted 49  •  71  tons. 

"  matte  slag        "     38-40    " 

Total..  .  88-11 


276     MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

Gas-coke  used 16'10tons. 

Assay  of  ore 3'87  per  cent. 

Assay  of  matte  slag 0  •  94        " 

Weight  of  matte  produced 20'67  tons. 

Assay  of  matte  produced 10-70  per  cent. 

Assay  of  slag  produced 0  •  13        " 

Bate  of  concentration,  about  2J  tons  of  ore  into  one.  The 
copper  produced  in  this  campaign,  after  taking  into  considera- 
tion the  metal  gained  in  the  matte  slag,  and  deducting  the 
small  amount  lost  in  the  slag  from  the  operation  itself,  agreed 
almost  exactly  with  the  amount  calculated  from  the  careful 
and  frequent  assays  made. 

The  matte  produced,  though  very  low  in  grade,  is  roasted 
in  heaps  with  great  facility,  and  forms  a  most  welcome  flux  for 
siliceous  ores. 

This  practice  is  unique  and  well  worthy  of  attention. 

The  size  to  which  ore  must  be  broken  for  cupola  smelting 
depends  upon  two  factors — its  fusibility  and  its  conductivity. 

Fusible  material,  especially  if  porous — such  as  ferrugin- 
ous and  calcareous  ores,  basic  slag,  etc. — may  be  charged  in 
fragments  from  3  to  5  inches  in  diameter  without  producing 
evil  results,  although  good  practice  demands  its  pretty  uniform 
reduction  to  the  size  of  a  large  apple  (that  is,  full  3").  The 
same  may  be  said  of  fragments  of  copper  matte  or  metallic 
substances,  which,  being  excellent  conductors  of  heat,  melt  all 
at  once,  where  a  piece  of  quartz  or  fire-clay  might  be  in  a  state 
of  fusion  on  the  surface,  while  hardly  heated  at  the  center,  and 
consequently  should  be  invariably  reduced  to  the  size  of  horse- 
chestnuts,  unless  smelted  in  company  with  a  large  proportion 
of  basic  ore.  A  striking  example  of  this  may  be  found  in  the 
fusion  of  "  mass  copper "  at  Lake  Superior,  where  pieces  of 
this  metal  weighing  five  or  six  tons  are  smelted  on  the  hearth 
of  a  reverberatory  furnace  with  no  difficulty  or  delay,  the  high 
conductive  power  of  copper  causing  an  equal  distribution  of 
heat  and  simultaneous  fusion  of  the  entire  mass.  A  rock  of 
the  same  size  could  never  be  smelted  except  by  the  gradual 
wearing  away  of  its  exterior  surface. 

The  following  resume  is  from  a  paper  on  Copper  Smelting 
by  H.  M.  Howe,  in  the  Bulletin  of  the  United  States  Geologi- 
cal Survey. 


GENERAL   REMARKS   ON  BLAST-FUENACE  SMELTING.        277 

KESUME. 

To  sum  up,  for  SMELTING  ORE  the  cupola  is  especially  advan- 
tageous— 

I.  With  highly  ferruginous  ores. 

II.  Where  the  cost  of  anthracite,  coke,  or  charcoal  is  not 
excessively  greater  than  that  of  bituminous  coal,  wood,  and 
other  fuels  fitted  for  the  reverberatory  only. 

III.  For  oxidized  ores. 

IV.  For  low-grade  native  copper. 

Y.     Where,  as  in  the  case  of  lean  ores,  clean  slags  are  a 

necessity. 

The  reverberatory  is  especially  advantageous — 

YI.  With  highly  refractory  siliceous,  aluminous,  calcareous, 

or  magnesian  ores. 

VII.  Where  the  composition  of  the  ore  changes  suddenly 
and  greatly. 

VIII.  Where  bituminous  coal,  wood,  or  other  reverbera- 
tory fuel  is  very  much  cheaper  than  anthracite,  coke,  or  char- 
coal. 

IX.  For  smelting  and  immediately  refining  rich  native  cop- 
per. 

X.  Its   disadvantage  in  yielding  richer  slags  than  the 
cupola  weighs  less  heavily  in  case  of  rich  ores. 


CHAPTER  XII. 

REVERBERATORY    FURNACES. 

THIS  method  of  smelting  copper  ores  is  peculiarly  English, 
the  reverberatory  furnace  having  practically  had  its  origin  in 
Swansea,  where  it  has,  during  the  past  two  centuries,  under- 
gone various  changes  and  improvements,  by  which  its  capacity 
and  economy  have  been  considerably  increased  without  any 
radical  alteration  in  its  original  form  or  practice. 

The  American  reverberatories  are  modeled  closely  after 
their  English  prototypes,  and  present  no  new  features  worthy 
of  note,  a  constant  tendency  toward  increased  size  and  capacity 
being  almost  the  only  point  in  which  any  difference  can  be 
detected. 

This  particular  branch  of  metallurgy  having  engaged  the 
attention  of  English  and  American  authors  to  a  greater  ex- 
tent than  any  other,  nothing  would  be  gained  by  a  mere .  repe- 
tition of  what  may  be  found  in  the  modern  text-books,  and  the 
writer  prefers  to  devote  his  own  work  to  those  practical  details 
of  construction  and  management  that  are  yet  wanting,  and 
which  he  hopes  may  supplement  the  more  strictly  scientific 
information  just  referred  to. 

While  the  blast-furnace  has  replaced  the  reverberatory  to 
a  considerable  extent  in  the  United  States  for  ore-smelting,  the 
latter  is  still  generally  preferred  for  matte  concentration,  and 
especially  in  its  last  stage,  or  the  production  of  "  blister  cop- 
per." 

The  processes  executed  in  the  reverberatory  furnace  in  this 
country  may  be  divided  into  the  following  classes,  each  of 
which  demands  separate  consideration  : 

1.  Ore  smelting. 

2.  Matte  concentration. 

a.  By  fusion  of  calcined  matte. 

b.  By  an  oxidizing  melting. 


KEVERBEEATORY   FURNACES.  279 

3.  Production  of  blister  copper. 

4.  Copper  refining. 

As  the  first  three  of  these  processes  are  carried  out  in  ex- 
actly the  same  type  of  furnace,  their  more  detailed  description 
may  well  be  preceded  by  some  consideration  of  the  construc- 
tion of  a  reverberatory  furnace. 

The  excavation  for  the  foundations  should  be  18  inches  in 
every  direction  larger  than  the  proposed  furnace,  allowance 
being  made  for  the  space  occupied  by  the  stack  or  down-take 
at  one  of  the  front  corners.  A  depth  of  4  feet  from  the 
floor  level  is  sufficient,  and  a  permanent  drain  should  keep  the 
pit  free  of  water.  Exceptional  circumstances  may  require  a 
greater  depth  of  so  much  of  the  excavation  as  corresponds  to 
the  foundation  of  the  stack.  Two  longitudinal  walls  are  now 
laid  in  such  a  manner  that  a  4-foot  space  is  left  under  the 
main  body  of  the  furnace,  extending  from  the  back  of  the  ash- 
pit to  a  point  directly  under  the  future  front  wall  of  the  furnace. 

This  is  arched  over  with  two  4-inch  courses  of  red  brick, 
upon  which  come  one  or  two  4^-inch  courses  of  fire-brick. 
The  bridge  wall  and  two  lateral  walls  of  the  ash-pit  are  also 
begun  from  the  same  level.  It  is  also  well  to  carry  up  the 
side  and  front  walls  of  the  furnace  from  the  very  bottom,  using 
red  brick  for  all  underground  work,  and  filling  the  space 
between  and  outside  of  the  walls  with  stone  or  slag,  broken  in 
situ  with  spalling-hammers,  and  firmly  united  with  liquid  mor- 
tar, or  by  pouring  in  the  pots  of  slag  as  they  come  from  the 
blast-furnace. 

It  is  quite  customary  to  fasten  the  looped  tie-rods  for  the 
perpendicular  buckstaves  by  merely  bending  a  hook  at  the  end 
of  the  rod  and  building  it  into  the  wall,  trusting  to  the  weight 
of  the  superincumbent  mason-work  to  prevent  their  drawing 
out.  It  is  a  much  safer  plan  to  introduce  the  tie-rods  at  a 
lower  level,  giving  them  sufficient  length  and  inclination  to 
pierce  one  of  the  central  longitudinal  walls,  and  providing  each 
with  an  eye  through  which  passes  a  long  continuous  bar  of 
iron,  which  thus  firmly  holds  all  the  tie-rods  belonging  to  one 
side  of  the  main  body  of  the  furnace.  This  bar  is  fastened  to 
its  fellow  of  the  other  side  by  a  few  short  cross-rods,  and  the 
lower  set  of  loops  is  thus  firmly  held  in  place,  and  far  below 


280     MODERN  AMERICAN  METHODS  OF   COPPER  SMELTING. 

any  chance  of  being  melted  in  two — an  accident  that  would 
certainly  occur  in  the  course  of  time  if  they  crossed  the  entire 
furnace  above  the  subterranean  arch. 

The  inclosing  walls  of  the  furnace  having  been  built  to 
within  a  foot  of  the  floor  surface,  the  hearth  proper  of  the  fur- 
nace is  laid  in  the  shape  of  an  inverted  arch,  its  lowest  point 
in  the  center  being  in  contact  with  the  upper  convex  surface 
of  the  4-foot  subterranean  arch,  while  its  sides  rise  at  the 
rate  of  about  half  an  inch  to  the  foot.  It  is  also  slightly  arched 
longitudinally,  and  should  be  well  keyed  and  grouted,  as  it  is 
intended  to  be  so  constructed  as  to  prevent  the  possibility 
of  its  being  floated  up  by  any  breaking  through  of  the  molten 
contents  of  the  sand-hearth. 

The  hearth  is  now  inclosed  by  side-walls  of  fire-brick,  4J 
inches  thick,  which  support  the  arch  when  the  proper  height  is 
reached.  These  are  incased  by  strengthening  walls  of  red 
brick,  while  they  are  protected  on  the  inside  by  a  9-inch  lining 
of  fire-brick,  which  can  thus  be  renewed  when  necessary 
without  interfering  with  the  arch. 

As  the  hearth  is  an  elongated  oval,  narrowing  to  about  18 
inches  at  the  skimming-door,  while  the  external  shape  is  usually 
that  of  a  rectangle,  it  follows  that  the  four  exterior  corners 
consist  of  useless  pillars  of  rubble  or  brick-work.  These  are 
sometimes  avoided  by  conforming  the  external  shape  to  that 
of  the  hearth,  and  inclosing  the  fire-brick  with  thin  wrought- 
iron  plates,  or  thicker  plates  of  cast-iron,  often  perforated  with 
rows  of  holes  to  diminish  their  weight.  The  latter  arrange- 
ment causes  some  difficulty  in  placing  the  buckstaves,  and 
presents  no  decided  advantage  over  the  older  plan  of  inclosing 
the  hearth  in  a  rectangular  mass  of  brick-work,  only  4  inches 
thick  at  the  widest  portion  of  the  hearth,  and  increasing  rapidly 
toward  each  extremity.  Two  heavy  vertical  cast-iron  plates 
support  the  hearth  at  each  end — the  "conker-plate"  giving 
strength  to  the  bridge- wall,  while  the  front  plate  is  placed  just 
below  the  front  door,  the  narrow  horizontal  skimming-plate 
resting  upon  it,  and  determining  the  eventual  thickness  of  the 
sand-bottom. 

The  bridge- wall  is  a  massive  structure  of  fire-brick,  perfo- 
rated by  an  air-passage  about  3  inches  by  10  inches,  which  has 


REVERBERATORY  FURNACES.  281 

the  conker-plate  for  its  anterior  wall,  while  a  lighter  casting 
forms  its  posterior  boundary.  A  large  blow-hole,  or  opening 
for  the  admission  of  air,  should  be  left  on  each  side  of  the  fur- 
nace in  the  angle  formed  by  the  posterior  wall  of  the  main 
portion  of  the  structure  and  the  wall  of  the  fire-box.  These 
orifices  are  used  only  when  an  oxidizing  atmosphere  is  desired, 
as  in  the  concentration  of  matte,  the  making  of  blister  copper, 
etc.,  and  can  be  tightly  closed  with  clay  under  ordinary  circum- 
stances. 

The  fire-box  is  inclosed  with  a  9-inch  wall  of  fire-brick, 
which  may  be  strengthened  by  a  casing  of  common  brick,  if 
desired. 

"Where  coal  is  used  for  fuel,  particular  attention  should  be 
given  to  placing  the  grating-holes  (that  is,  the  orifices  in  the 
sides  of  the  fire-box  just  above  the  grate,  through  which  bars 
are  introduced  to  cut  away  the  clinkers)  in  a  convenient  posi- 
tion. 

The  arch  is  best  constructed  of  "  Dinas "  or  silica  brick, 
which  last  much  longer  than  ordinary  fire-brick,  and  should 
have  a  rise  of  an  inch  to  the  foot,  pitching  downward  quite 
abruptly  from  a  point  slightly  anterior  to  the  bridge-wall,  until 
it  approaches  to  within  twelve  or  fourteen  inches  of  the  skim- 
ming-plate at  the  front  door.  Its  shape,  as  well  as  the  size 
and  proportions  of  the  space  between  bridge  and  roof,  has 
much  to  do  with  the  heating  qualities  of  the  furnace,  and  must 
vary  with  the  character  of  the  fuel  and  with  other  local  condi- 
tions. The  extreme  front  row  of  arch  bricks,  forming  the 
posterior  wall  of  the  flue  opening  in  the  roof,  is  called  the 
"  vulcatory,"  and  from  its  situation  is  so  exposed  to  wear  and 
heat  as  to  require  frequent  renewal. 

The  flue  opening  itself  is  of  a  trapezoidal  form,  being 
inclosed  laterally  between  the  two  converging  walls  of  the 
hearth,  while  it  has  the  vulcatory  for  its  posterior  and  the 
front  wall  of  the  furnace  for  its  anterior  boundary. 

Its  size  and  proportions  are  matters  of  paramount  import- 
ance, as  the  heating  capacity  of  the  furnace  as  well  as  its 
consumption  of  fuel  depends  principally  upon  it  and  upon  the 
size  and  shape  of  the  flue  proper,  that  is,  the  canal  connecting 
the  hearth  with  the  chimney. 


282     MODERN   AMERICAN  METHODS   OF  COFFEE  SMELTING. 

No  precise  rules  can  be  laid  down  in  this  matter  for  the 
guidance  of  the  inexperienced,  as  each  individual  case  must  be 
judged  upon  its  own  merits  until  constant  experimenting  has 
determined  the  question. 

The  uncertainty  and  difficulty  pertaining  to  this  matter  may 
be  best  appreciated  when  it  is  known  that,  of  half  a  dozen 
furnaces  in  the  same  building,  constructed  from  the  same  plan 
and  apparently  identical  in  every  particular,  fed  with  the  same 
fuel,  and  smelting  the  same  ore,  no  two  behave  in  the  same 
manner,  and  therefore  each  differs  in  size  and  shape  of  flue. 
In  general  terms,  it  may  be  stated  that  a  large  flue  will  cause 
a  greater  consumption  of  fuel  and  a  quicker  heat,  unless  a 
certain  limit  is  over-stepped,  beyond  which  the  fuel  will  be 
burned  without  a  corresponding  rise  of  temperature.  It  is 
quite  obvious,  therefore,  that  the  economical  smelter  will  seek 
to  throttle  his  flue  to  the  greatest  possible  extent  compatible 
with  the  rapid  production  of  the  required  temperature.  The 
flue  should  be  narrowest  at  its  junction  with  the  furnace,  and 
expand  considerably  as  it  enters  the  stack,  having  at  least  50 
per  cent,  greater  area  at  the  latter  point  than  at  the  former. 
Its  size  is  altered  by  introducing  or  removing  a  little  dam  of 
sand  at  the  end  nearest  the  furnace,  one  of  the  slabs  with  which 
it  is  covered  being  removed  for  that  purpose.  When  experi- 
ments of  this  nature  are  executed  to  determine  the  most 
advantageous  flue  area,  it  is  important  that  the  change  in  size 
be  sufficient  to  produce  some  plainly  marked  effect  either  for 
the  better  or  the  worse  ;  otherwise,  it  is  a  mere  groping  in  the 
dark.  The  weather,  force  or  direction  of  the  wind,  and  general 
condition  of  the  atmosphere  may  often  produce  an  impression 
sufficiently  powerful  to  entirely  mask  the  changes  brought 
about  by  the  alteration  of  the  flue  area,  so  that  a  considerable 
period  may  be  necessary  to  properly  estimate  the  good  or  evil 
resulting  from  the  efforts  of  the  smelter.* 

The  buckstaves  supporting  the  furnace  should  be  of 
wrought-iron,  and  sufficiently  strong  and  numerous  effectually 
to  prevent  any  spreading  of  the  sides  or  arch. 

*  The  proportions  of  numerous  reverberatory  furnaces  are  given  in  Egles- 
ton's  monograph  on  Copper  Refining  in  the  United  States,  as  well  as  in  a 
vauable  paper  by  H.  M.  Howe,  E.  M.,  in  the  government  report,  edited  by 
Albert  Williams,  Jr. 


REVERBERATORY  FURNACES.  283 

This  is  especially  important  with  blister  or  refining-furnaces, 
where  the  weight  of  the  molten  bath  may  amount  to  10  or  15 
tons,  which,  combined  with  the  lateral  pressure  caused  by  the 
high  temperature,  produces  an  expansive  force  that  is  almost 
incredible. 

The  tie-rods  should  be  of  IJ-inch  square  iron,  provided  at 
the  extremities  with  loops,  and  not  with  thread  and  nut. 

Where  wood  is  used  as  a  fuel,  a  row  of  small  openings 
should  be  left  in  the  arch  over  the  anterior  edge  of  the  fire- 
bridge ;  an  arrangement  that  insures  the  combustion  of  the 
gases  in  the  hearth  where  they  are  needed,  instead  of  in  the 
chimney,  where  they  may  produce  a  most  detrimental  effect, 
destroying  the  fire-brick  lining  within  a  few  days. 

Even  with  this  precaution,  it  is  sometimes  necessary  to 
leave  an  opening  near  the  base  of  the  stack,  to  prevent  excess- 
ive flaming  just  after  adding  fresh  fuel. 

A  damper  playing  in  a  hinge,  and  fastened  to  a  cast-iron 
frame,  should  invariably  be  placed  on  the  summit  of  the  stack. 
By  this  means,  the  draught  can  be  effectually  regulated,  or 
entirely  cut  off  if  desired — as  when  charging  fine,  dry  ore — 
without  resorting  to  the  familiar  but  slovenly  practice  of 
removing  a  slab  from  the  flue  and  inserting  an  iron  plate. 

The  capacity  of  a  reverberatory  furnace  and  that  quality  of 
rapid,  fierce  heating  so  essential  to  economical  ore  smelting, 
are  largely  dependent  upon  the  proportions  of  the  flue  and 
stack,  and  while  the  former  may  easily  be  made  too  large  for 
economical  work,  the  latter  is  oftener  too  small  for  the  sharp 
draught  required. 

These  remarks  apply  especially  to  reverberatories  used  for 
smelting  ore,  where  the  object  is  to  attain  the  highest  possible 
temperature  in  the  shortest  time.  Blister  furnaces,  or  those 
devoted  to  matte  concentration  by  the  old  method  of  "  sweat- 
ing down,"  do  not  require  such  a  powerful  draught,  as  the 
processes  are  slow,  and  the  temperature  required  comparatively 
low.  For  this  reason,  they  may  be  provided  with  down-takes 
and  flues  entering  a  stack  common  to  several  furnaces ;  while 
each  ore-smelting  reverberatory  should  have  its  own  independ- 
ent stack,  without  either  flue  or  dust-chambers ;  any  loss  in 
flue-dust  that  may  occur  after  closing  the  damper  while  charg- 


284     MODERN  AMERICAN   METHODS   OF   COPPER  SMELTING. 

ing  being  fully  counterbalanced  by  the  saving^in  time  and  fuel, 
except  under  peculiar  circumstances. 

The  fire-brick  lining  should  be  entirely  independent  of  its 
surrounding  walls,  so  that  it  can  be  easily  removed  and  re- 
newed, and  a  2-inch  air-space  should  be  left  between  the  same, 
connecting  with  openings  near  the  base,  so  that  a  current  of 
cool  air  may  constantly  surround  the  heated  lining. 

As  has  been  already  mentioned,  that  portion  of  the  stack 
below  the  entrance  of  the  lateral  flue  should  be  left  entirely 
empty  nearly  to  the  ground  level,  in  order  that  an  elastic 
cushion  may  be  provided  for  the  flame  as  it  enters  the  stack 
from  the  furnace. 

The  height  of  the  stack  need  seldom  exceed  56  feet,  unless 
local  conditions  affect  the  draught.  The  immediate  proximity 
of  higher  roofs  or  abrupt  hills  often  injures  the  draught  to  a 
most  serious  extent,  which  circumstance  should  always  be 
borne  in  mind  in  planning  new  works. 

From  a  stack  65  feet  high,  the  writer  has  removed  15  feet, 
and  subsequently  added  30  feet,  without  affecting  the  working 
of  the  furnace  in  the  slightest  degree ;  but  the  height  just 
mentioned  may  be  regarded  as  safe  under  ordinary  circum- 
stances. 

The  position  of  the  large  doors  and  other  openings  of  the 
building  should  be  so  arranged  that  under  no  conditions  can 
the  wind  blow  across  the  ash-pit  of  the  furnace  in  such  a  man- 
ner as  to  counteract  the  draught.  It  is  not  uncommon  to  find 
furnaces  that,  during  certain  winds  and  other  atmospheric  in- 
fluences fall  off  to  a  very  marked  degree  in  their  duty. 

There  should  be  an  ample  free  space  about  a  reverberatory 
furnace ;  at  least  15  feet  on  the  tapping  side,  and  the  same 
distance  in  front,  while  a  space  of  12  feet  on  the  charging-door 
side  will  suffice.  This  should  be  well  drained  and  paved  with 
brick  on  edge,  or  with  cast-iron  plates. 

The  arch  being  completed  and  the  wooden  pattern  re- 
moved, the  furnace  is  taken  in  charge  by  the  smelter,  who, 
with  the  blacksmith's  aid,  proceeds  to  the  proper  tightening  of 
the  tie-rods ;  the  side  buckstaves  having  been  already  suf- 
ficiently drawn  up  to  keep  the  arch  in  place.  This  process 
has  been  described  in  the  chapter  on  Calcining  Furnaces,  and 


REVERBERATORY   FURNACES. 


285 


presents  no  peculiarities.  The  empty  hearth  should  be  cov- 
ered with  a  2-inch  layer  of  fire-clay,  to  prevent  adhesion  of 
any  metal  that  may  possibly  make  its  way  through  the  sand 
bottoms. 

A  small  fire  may  be  at  once  built  on  the  surface  of  the  clay 
stratum  and  in  the  ash-pit,  and  should  be  maintained  for  at 
least  four  days,  slightly  raising  the  temperature,  until,  at  the 
expiration  of  this  time,  a  dark-red  heat  is  attained,  and  the 
cessation  of  aqueous  vapors  from  the  side  walls  and  subter- 
ranean arch  shows  that  every  particle  of  moisture  is  removed. 

The  grate-bars  are  now  placed  in  position — being  mere 
rods  of  inch-square  wrought- iron — and  the  fire  being  shifted  to 
its  proper  position,  is  gradually  urged  for  twelve  hours  or 
more,  until  the  whole  interior  is  of  a  light-red  heat. 

Then,  and  not  until  then,  should  the  material  for  the 
smelting-hearth  be  introduced. 

This  consists  essentially  of  silica,  and  may  be  in  the  shape 
of  well-washed  beach  sand,  or  crushed  sandstone,  or  of  pulver- 
ized quartz,  first  roasted  in  lumps  and  quenched  while  hot,  to 
impart  a  high  degree  of  brittleness  and  greatly  facilitate  its 
crushing. 

A  beach  sand  employed  for  this  purpose  in  Swansea,  and 
analyzed  by  Percy,  had  the  following  composition : 


Per  cent. 

Silica 87-87 

Alumina 2*13 

Sesquioxide  of  iron 2*72 

Lime  . .  3*79 


Per  cent. 

Magnesia 0'21 

Carbonic  acid  and  water 2 '60 

Total  .  .  99-32 


This  is  not  so  refractory  as  the  crushed  sandstone  employed 
by  some  of  the  Eastern  American  smelting-works,  or  the  pul- 
verized quartz  used  for  reverberatory  bottoms  in  Butte,  Mon- 
tana, which,  according  to  the  author's  tests,  contain  respect- 
ively, when  dry,  95*3  per  cent,  and  97*2  per  cent,  of  insoluble 
residue,  presumably  silica. 

Two  methods  are  pursued  in  making  reverberatory  hearths : 
Either  the  sand  chosen  contains  enough  bases  to  be  slightly 
fusible,  or  a  small  proportion  of  crushed  slag  or  other  similar 
substance  is  added  so  that  the  sand  may  become  slightly 
agglomerated  by  the  intense  heat  to  which  it  is  subjected ;  or 


286     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

secondly,  the  material  selected  is  practically  infusible,  and  the 
cementation  of  its  particles  is  effected  by  smelting  small  and 
repeated  charges  of  fusible  material  upon  the  slightly  hard- 
ened surface  of  the  same,  until  it  is  solidified  into  a  hard  and 
impermeable  mass. 

The  author  prefers  a  combination  of  these  two  systems, 
using  the  first  method  for  the  lower  hearth,  and  the  second  for 
the  upper  or  true  hearth ;  as  it  is  usual  to  put  in  two  separate 
hearths,  the  upper  one  being  comparatively  thin,  so  that  it  can 
be  easily  removed  when  worn  out. 

The  total  height  from  the  floor  of  the  furnace  to  the  upper 
surface  of  the  skim-plate  being  perhaps  30  inches,  the  lower 
hearth  (including  the  clay  bottom)  should  have  a  thickness  of 
18  inches  and  the  upper  of  12  inches,  both  of  them  being 
somewhat  concave  in  shape,  so  that  a  basin  is  formed  some  5 
inches  deeper  than  the  skim-plate  in  the  center,  and  sloping 
from  every  direction  toward  the  tap-hole. 

The  size  of  the  hearth  material  is  a  matter  of  less  import- 
ance than  is  often  supposed,  provided  that,  if  at  all  coarse, 
sufficient  fine  dust  is  present  to  fill  all  interstices  and  pre- 
vent porosity. 

If  good  crushing  facilities  can  be  had,  it  is  well  to  pass 
everything  through  a  16-mesh  screen,  but  the  author  has  used 
even  a  5-mesh  without  evil  results. 

This,  of  course,  refers  to  sandstone  or  quartz  rock.  Natural 
sand  usually  requires  no  sizing  process,  unless  mixed  with  gravel. 

The  utmost  care  should  be  taken  to  prevent  the  introduc- 
tion of  any  foreign  material,  especially  of  an  organic  nature,  as 
the  gases  generated  therefrom  may  easily  cause  a  ruinous  flaw 
or  blister  in  an  otherwise  perfect  hearth. 

Such  unfortunate  results,  however,  are  usually  counter- 
acted by  the  thorough  calcination  that  all  sand  must  undergo 
previous  to  the  final  smelting. 

A  sufficient  amount  of  the  sand — usually  from  4  to  5  tons 
— being  thrown  into  the  heated  furnace  (either  as  such,  or 
mixed  with  from  3  to  5  per  cent,  of  pulverized  slag),  a  mod- 
erate fire  is  maintained,  while  a  steady  stirring  and  rabbling 
is  kept  up  through  the  side  and  front  doors,  until  every  par- 
ticle of  moisture  and  carbonic  acid  and  other  gases  is  expelled, 


REVERBERATORY   FURNACES.  287 

and  the  beat  gradually  raised  to  such  a  temperature  as  to  in- 
sure the  decomposition  of  all  organic  material.  This  operation 
may  require  from  3  to  8  hours,  according  to  the  nature  of  the 
material.  Both  the  temperature  and  time  are  matters  of  great 
importance,  having  a  marked  effect  upon  the  final  result ;  but 
can  only  be  learned  by  experience,  as  they  vary  with  each 
different  sand. 

Toward  the  close  of  this  period,  the  sand  is  gradually 
brought  into  the  proper  shape  for  the  bottom,  and  thoroughly 
pressed  and  stamped  into  place  by  means  of  long  paddles  and 
stampers,  worked  through  the  door  openings.  No  great  pains 
need  be  expended  upon  the  lower  hearth,  as  it  will,  of  course, 
be  entirely  covered  and  its  shape  obliterated  by  the  superior 
layer. 

The  doors  are  then  closed ;  the  tap-hole  bricked  up  and 
covered  with  a  heap  of  sand,  and  every  crack  and  orifice  about 
the  whole  furnace  completely  stopped  and  closed.  The  fire  is 
gradually  urged  until  the  highest  possible  temperature  is 
reached  and  maintained  for  a  couple  of  hours,  the  entire  period 
of  heating  requiring  from  6  to  14  hours,  according  to  the  heat- 
ing capacity  of  furnace  and  fuel.  The  interior  condition  of 
affairs  is  watched  through  a  peep-hole  in  the  front  door,  which 
is  provided  with  a  clay  plug.  After  a  proper  maintenance  of 
the  highest  temperature,  the  fire  is  gradually  slackened  and 
the  furnace  cooled  down.  This  operation  demands  the  great- 
est care  and  circumspection,  as  the  premature  opening  of  a 
door  or  a  sudden  draught  of  cold  air  may  cause  the  appear- 
ance of  a  crack  or  blister  in  the  porcelain-like  surface  of  the 
sand  hearth.  Several  hours  must  elapse  before  the  doors  can 
be  taken  down  and  the  results  of  the  operation  inspected. 
The  interior  of  a  reverberatory  furnace  under  these  circum- 
stances is  quite  an  interesting  sight. 

Long  stalactites  of  molten  fire-brick  hang  down  from  the 
arch  over  its  entire  surface.  The  side  walls  are  not  only 
glazed,  but  actually  fused  until  they  have  begun  to  soften  to  a 
considerable  depth,  and  the  hard  and  glistening  semi-fused 
surface  of  the  new  hearth  is  strewn  with  fragments  of  brick 
from  the  crown,  and  little  heaps  of  molten  fire-clay  correspond- 
ing to  the  pendent  stalactites. 


288      MODERN  AMEKICAN  METHODS   OF  COPPER  SMELTING. 

Unless  very  serious  cracks  exist,  no  notice  need  be  taken 
of  them,  and  blisters  and  irregularities  may  be  entirely  over- 
looked, as  the  upper  hearth  is  to  bear  the  brunt  of  the  work. 
After  slow  and  perfectly  even  cooling  to  a  dark-red  heat, 
about  1800  pounds  of  moderately  basic,  fusible  slag,  crushed 
to  the  size  of  chestnuts,  is  spread  over  the  entire  surface,  be- 
ing charged  by  means  of  long-handled  paddles,  and  on  no 
account  thrown  in  carelessly,  to  be  subsequently  leveled  with 
rabbles,  as  is  often  done.  The  doors  being  again  tightly 
closed,  the  slag-charge  is  quickly  smelted  down,  two  hours  be- 
ing amply  sufficient  for  this  purpose.  This  layer  of  slag  will 
be  entirely  absorbed  by  the  porous  sand  bottom,  which,  after  a 
second  cautious  cooling,  should  be  again  charged  with  a  some- 
what larger  burden  of  slag,  with  which  are  mixed  a  few  hun- 
dred pounds  of  low-grade  matte  (30  per  cent.).  After  this  is 
melted  down,  a  considerable  portion  will  probably  be  found 
in  a  pool  near  the  tap-hole,  from  which  it  should  be  immedi- 
ately evacuated.  If  the  furnace  is  to  be  used  for  concentra- 
tion work,  or  especially  for  the  production  of  blister  copper, 
still  another  charge  should  be  melted  on  the  lower  hearth, 
consisting  principally  of  matte  of  the  same  grade  as  the  former, 
and  should  be  tapped  as  soon  as  sufficiently  liquid.  In  this 
way,  the  lower  hearth  will  be  pretty  thoroughly  saturated  with 
matte  of  low  tenor,  thus  preventing  the  absorption  of  an  equiv- 
alent quantity  of  richer  metal  in  case  the  same  shoulfl  pene- 
trate from  the  upper  hearth.  The  tying  up  of  a  large  amount 
of  copper  may  thus  be  guarded  against. 

After  a  final  cooling,  the  sand  to  form  the  upper  hearth  is 
thrown  in,  and,  after  a  careful  calcining  and  leveling,  should 
be  stamped  into  place  with  the  utmost  care,  sloping  gently 
toward  the  tap-hole  from  every  point. 

The  fusion  is  executed  in  the  manner  already  described, 
and  in  addition  a  careful  watch  should  be  maintained  at  the 
peep-hole  to  observe  any  fragments  of  brick  that  may  fall  from 
the  arch  during  the  early  period  of  the  fusion.  After  the  soft- 
ening of  the  sand  has  once  begun,  no  further  manipulation  is 
permissible. 

The  cooling  after  the  fusion  must  be  executed  with  extreme 
care,  to  prevent  cracking  and  blistering,  and  as  soon  as  a  dull- 


REVERBERATORY  FURNACES.  289 

red  heat  is  reached,  the  slag  and  matte  charges  already  enu- 
merated should  be  successively  melted,  with  alternate  periods 
of  cooling. 

As  a  final  preparation  before  introducing  the  first  ore- 
charge,  a  small  quantity  of  finely  crushed  slag  should  be 
thrown  around  the  entire  edge  of  the  hearth  at  the  junction  of 
sand  and  fire-brick. 

Above  this,  a  thick  bolster  of  "  fettling "  (mixed  fire-clay 
and  crushed  quartz)  should  be  tightly  forced  into  the  angle 
between  hearth  and  side-walls,  including  the  bridge-wall. 

An  hour's  brisk  heat  will  dry  and  consolidate  the  fettling,  and 
the  regular  work  of  the  furnace  may  begin — small  charges  being 
used  at  first,  and  no  large  quantity  of  metal  allowed  to  accumulate 
before  tapping. 

MANAGEMENT  OF   FURNACE. 

The  experienced  furnace-man  constantly  watches  his  fur- 
nace with  reference  to  the  safety  and  condition  of  its  bottom. 
After  a  few  hours'  firing  on  a  fresh  charge,  the  workman  intro- 
duces his  rabble,  and  by  the  feeling  of  the  sand  when  gliding 
over  the  bottom,  determines  at  once  the  condition  of  things. 

If  slippery  and  sticky,  it  indicates  that  portions  of  the 
charge  still  adhere  to  the  hearth.  These  are  removed  as  far 
possible  by  the  rabble,  and  dissolved  by  a  short  additional 
heat,  until  the  rabble  glides  smoothly  over  a  plane,  granular 
bottom,  which  is  the  upper  surface  of  the  hearth  proper. 
After  this  condition  is  once  attained,  every  additional  moment 
of  high  temperature  is  not  only  wasted,  but  is  positively  detri- 
mental to  the  hearth,  which  lacks  the  protection  of  the  semi- 
fused  ore,  the  liquid  matte  soon  attaining  a  high  temperature, 
and,  if  exposed  to  the  air,  boiling  in  a  manner  that  may  prove 
highly  dangerous  to  the  bottom.  This  is  the  case  when  con- 
centrating matte  or  making  blister  copper — operations  very 
severe  on  the  bottom,  but  rendered  less  dangerous  by  being 
conducted  at  a  lower  temperature  than  is  required  for  smelting 
proper. 

Equally  detrimental   may  be  a  high  temperature  with  a 
small  charge,  where  the  unprotected  portions  of  the  bottom 
may  become  so  softened  as  to  rise  in  large  flakes,  being  lite- 
rally floated  up  by  the  superincumbent  metal. 
19 


290     MODEEN  AMERICAN  METHODS  OF   COPPER  SMELTING. 

Any  large  piece  of  iron,  such  as  a  rabble-head,  may  cause  a 
hole  in  the  bottom,  and  in  endeavoring  to  float  up  an  old  bot- 
tom, nothing  is  more  effective  than  the  introduction  of  a  num- 
ber of  large  fragments  of  old  iron.  A  bottom  may  be  often 
patched  to  advantage  when  only  locally  damaged.  "When  any 
such  condition  is  discovered,  the  hearth  should  be  immediately 
emptied,  and  the  damaged  portion,  which  usually  shows  a  de- 
cided cavity  or  depression,  should  be  most  carefully  emptied, 
fresh  sand  being  repeatedly  introduced  and  again  removed 
with  the  rabble  until  it  is  completely  dry.  The  hole  should 
then  be  filled  and  leveled  up  with  ordinary  bottom  sand,  which 
must  be  fused  and  saturated  with  the  same  precautions  as  in 
the  case  of  the  original  bottom.  In  this  way,  a  bottom  may 
often  be  saved  for  many  months  at  a  very  slight  expense. 

In  direct  connection  with  the  management  of  the  bottom  is 
the  proper  fettling  of  the  furnace.  The  entire  life  of  the  side 
walls  and  safety  of  the  bottom  depend  upon  the  care  and  consci- 
entiousness observed  in  maintaining  the  dam  that  incloses  the 
molten,  liquid  pool  and  protects  the  fire-brick.  In  default  of 
this  safeguard,  the  side  walls  are  quickly  undermined,  a  groove 
several  inches  in  depth  being  cut  into  the  mason- work  during 
the  smelting  of  a  single  basic  charge.  Nothing  then  remains 
to  prevent  the  descent  of  the  metal  between  the  wall  and  bot- 
tom until  the  latter  is  floated  up  and  ruined,  and  a  large  amount 
of  copper  temporarily  lost.  The  best  fettling  is  formed  of 
pure,  white  quartz,  crushed  through  a  3-mesh  screen  and  mixed 
with  sufficient*  plastic  fire-clay  to  form  balls,  which  may  be 
placed  at  exactly  the  required  point,  and  forcibly  pressed  and 
molded  into  place.  The  quartz  may  be  replaced  by  ordinary 
bottom  sand,  which,  however,  is  less  permanent  and  solid. 
When  smelting  basic  ore,  the  hearth  may  require  fettling  after 
every  charge  ;  but  with  a  quartzose  mixture,  days  may  elapse 
without  any  necessity  for  renewal.  Safety  in  this  particular  is 
only  obtained  at  the  expense  of  constant  watchfulness. 

The  size  of  the  fire-box  and  depth  of  grate  below  the  upper 
surface  of  the  bridge  are  very  variable  factors,  depending  upon 
the  quality  of  the  fuel  and  degree  of  temperature. 

The  best  and  most  economical  results  are  obtained  by  the 
use  of  the  clinker  grate,  which  is  virtually  a  gas  generator,  a 


REVERBEEATORY   FURNACES. 


291 


deep  layer  of  clinkers  being  maintained  upon  the  grate-bars, 
penetrated  by  numerous  openings  through  which  the  air  passes, 
being  heated  to  a  high  temperature  before  it  unites  with  the 
gas  generated  from  the  coal,  which  lies  upon  the  upper  surface 
of  the  bed.  A  certain  proportion — from  one-third  to  one-half 
— of  caking  coal  is  required  for  this  method  of  combustion,  and 
the  grate-bars  must  be  at  a  much  greater  depth  than  for  ordi- 
nary non-caking  fuel. 

Lignites,  or  any  free-burning,  non-caking  coal,  require  a 
shallow  grate  and  a  large  flue,  while  wood  behaves  in  much 
the  same  manner,  requiring,  however,  the  introduction  of  air 
through  holes  in  the  roof  above  the  bridge,  on  account  of  the 
great  volume  of  combustible  gases  generated. 

It  is  almost  impossible  to  give  any  general  rule  for  the 
amount  of  fuel  required  for  a  reverberatory  furnace.  When 
engaged  in  smelting  ores,  a  much  larger  quantity  must  be  con- 
sumed than  in  making  blister  copper  or  in  the  refining  process, 
where  only  a  very  moderate  temperature  is  needed  for  a  con- 
siderable portion  of  the  time.  The  following  table  gives  the 
average  results  obtained  by  the  writer,  and  comprises  several 
varieties  of  fuel,  and  most  of  the  different  operations  executed 
in  the  reverberatory  furnace  : 


TABLE  OF  REVERBERATORY  WORK. 


OPERATION. 

Fuel. 

Size  of  fire-box 
in  feet. 

Size  of  hearth. 

Fuel  nsed  per 
twenty-four 
hours. 

Ore  smelting.  . 
Same  furnace  . 

Same  furnace. 
Ore  smelting.  . 

Blister    smelt- 
ingr.  . 

Lignite. 

Bituminous 
coal. 
Wood. 
Bituminous 
coal. 
Bit  uminoup 
coal 

31  x  4 

3i  x  4 
3i  x  4 

3^  x  4 
3£  x  4 

9  x  14^ 

9  x  14i 
9  x  14£ 

10  x  15 
10  x  15 

5^  tons 

3|  tons 
6i  cords 

3|  tons 
24-  " 

Blister     smelt- 
ing   

Wood. 

3i  x  4 

10  x  15 

4^  cords 

Refining   .  .  . 

Wood 

32  x  4^ 

9  x  13£ 

5     " 

Refining  

Coal. 

3|  x  4 

9£  x  14 

3    toes 

One  ton  =  2,000  pounds. 

Anthracite  may  be  employed  in  this  form  of  furnace,  when  provided  with 
a  tight  fire-box  and  an  artificial  blast  of  considerable  volume  and  slight 
pressure. 


292     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

ESTIMATE    OF  LABOR    AND    MATERIALS    FOR  BUILDING    AN    OR- 
DINARY REVERBERATORY  FURNACE. 

Size  of  hearth  inside,  9J  by  14  feet.  Besides  the  indepen- 
dent 9-inch  lining  of  fire-brick,  inclosing  the  hearth,  there  is  a 
backing  of  4J  inches  of  fire-brick,  from  which  the  arch  takes 
its  spring,  and  a  casing  of  red  brick,  12  inches  thick  at  the 
widest  part  of  the  hearth,  and  rapidly  increasing  in  thickness 
toward  either  end.  The  fire-box  is  3J  by  4  feet,  and  the 
bridge  30  inches  across. 

All  these,  as  well  as  the  remaining  proportions,  may  be 
altered  within  ordinary  limits,  without  materially  affecting  this 
estimate. 

Detailed  drawings  of  the  best  reverberatories  are  acces- 
sible to  all,  and  nothing  would  be  gained  by  a  repetition  of 
these  illustrations. 

EXCAVATION  FOR  FOUNDATIONS. 

This  should  be  about  18  inches  larger  in  every  direction 
than  the  proposed  stone  foundations,  and  about  3  feet  9  inches 
deep  ordinarily,  while  the  excavation  for  the  stack  foundation 
is  put  at  6  feet  deep.  The  amount  of  earth  usually  removed 
is  about  1,940  cubic  feet,  costing,  to  dig  and  remove,  about  2J 
cents  per  cubic  foot.  Total,  $49.50. 

STONE  WORK. 

The  stone  foundation  walls  are  usually  continued  to  within 
about  8  inches  of  the  surface  of  the  ground,  and  will  require 
about  700  cubic  feet  of  stone  work,  which  includes  the  stack- 
foundation  complete  at  35  cents  per  cubic  feet  2 =$245. 

BRICK  WORK. 

Tlie  fire-brick  required  will  be  :  Cubic  feet. 

For  lowest  fire-brick  arch  over  4-foot  vault 25 

Main  concave  arch,  forming  bottom 114 

Front  wall  at  skimming-door 6 

FJue  and  covering  slabs 22 

Bridge- wall,  estimated  as  if  solid 35 

Two  side  walls  of  fire-box 110 

Rear  wall  of  fire-box 15 

Hearth  lining 100 

Carried  forward. . ,  42? 


REVERBERATORY  FURNACES.  293 

Brought  forward 437 

Lining  of  stack,  estimated  at  14  inches  thick  for  lower  half 
and  4£  inches  for  upper  half,  stack  60  feet  high,  and  as- 
sumed to  be  32  inches  square  in  the  clear  throughout, 
to  simplify  calculation 690 

Total  cubic  feet 1;117 

Assuming  18  fire-bricks  to  the  cubic  foot,  we  have  a  total 
of  square  fire-brick  of  20,106.  To  these  must  be  added  the 
following  so-called  "  shaped  brick,"  to  avoid  cutting  in  turning 
arches,  door-jambs,  etc.,  and  in  laying  skew-backs. 

No.  of  brick. 

Bull-heads 250 

Side  skewbacks 250 

Jamb-brick 60 

Wedge  brick 30 

Soaps 80 

Splits 80 

Total 750 

Added  to  the  square  brick  =  grand  total 20,856 

Say  21,000  at  $40  per  thousand $840.00 

The  main  arch  of  the  furnace  will  require  2,000  Dinas 
brick  at  $60  per  thousand $120.00 

FIRE-CLAY. 

For  laying  the  above  brick  will  be  required  : 

Raw  fire-clay,  5  tons  at  $8 $40.'00 

Burnt  fire-clay,  5  tons  at  $8 40.00 

$80.00 

ORDINARY  CLAY. 

10  loads  at  $2 $20.00 

The  red  brick  required  are  .  Cubic  feet. 

For  side  walls  of  vault  under  furnace 192 

For  double  4-inch  arches  over  vault 43 

Front  wall  under  skim-door 84 

Side  casing  walls  and  solid  corners 408 

Side  casing  walls  of  fire-box  and  ash-pit 128 

855 

Casing  of  50-foot  stack,  assuming  it  to  average  12  inches 
thick  for  the  entire  distance.  1,260 


Grand  total 2,115 


294      MODERN  AMERICAN   METHODS   OF  COPPER  SMELTING. 

Assuming  25  brick  per  cubic  foot — to  allow  for  waste, 
we  have  total  number  of  red  brick,  52,785— say  53,00 
at  $8 $424.00 

LIME,  SAND,  AND  CEMENT. 

To  lay  the  above  brick  require : 

50  barrels  lime  at  $1  . $50. 00 

12  barrels  cement  at  $1.50 18.00 

25  loads  sand 36.50 

Total $105.50 

IRON  WORK. 

Assuming  that  no  proper  expense  is  to  be  spared,  the  fol- 
lowing iron  work  is  required,  being  somewhat  heavier  than  is 
commonly  used ;  though  no  more  than  is  needed  for  a  strong 
and  permanent  furnace.  Most  of  these  plates  are  ribbed  to 
increase  their  strength. 

Bridge  plate,  5  feet  long,  32  inches  high,  3  inches  thick,  Pounds. 
tapered  and  cored  with  holes  to  lessen  weight 1,120 

Front  plate  (across  entire  front  and  below  skimming  door), 
6  feet  3  inches  long,  2  feet  high,  3  inches  thick, 
tapered  and  perforated 1,110 

Ribbed  plate  to  support  rear  wall  of  fire-box,  5  feet  long, 

9  inches  wide,  1  inch  thick,  with  heavy  rib  on  top 182 

Bibbed  plate  to  support  the  fire-  box  portion  of  bridge- 
wall,  5  feet  long,  9  inches  wide,  1£  inches  thick 246 

Bear  bridge-plate,  which  forms  rear  wall  of  air  channel 
through  bridge,  5  feet  long,  2  feet  8  inches  high,  and 
2  inches  thick  (tapering) 500 

Plate  to  support  one  end  of  fire-box  and  contains  frame 
for  sliding  door,  32  inches  wide,  36  inches  high,  1  inch 
thick 200 

Skimming-block,  forming  threshold  of  skimming-door, 
and  easily  removable,  26  inches  long,  8  inches  wide  on 
top  and  5  inches  below,  and  10  inches  high 430 

Plate  to  protect  brick-work  at  side-door  with  opening  for 
door,  6  feet  9  inches  long,  5  feet  high,  I  inch  thick.  725 

4  skewback  plates  on  main  furnace,  above  and  below, 
each  17  feet  long,  4  inches  wide,  1  inch  thick,  with 
heavy  rib 1,061 

Plate  to  support  flue,  3  feet  long,  24  inches  wide,  1  inch 
thick,  with  light  ribs 246 

Chimney  cap  and  d.amper 549 

Frames  for  fire-door  and  charging-door 181 

2  bearing  bars  for  grates  and  1  grating  bar,  5  feet  long 
and  2  by  3  inches  wide 305 


Total  cast-iron  for  reverberatory  furnace 6,865 


EEVERBEEATOEY   F (JEN ACES.  295 

WROUGHT  IRON. 

Tie-rods  of  14  inches  round  iron.  Feet.       Pounds. 

9  upper  and  9  lower  across  main  part  of  furnace. .  252 

3  upper  across  fire-box 24 

2  upper  longest 45 

2  upper  longitudinal  on  main  furnace 34 

2  upper  uniting  in  ring 16 

7  lower  hooks  in  fire-box 18 

2  lower  hooks  at  end  of  fire-box 12 

2  lower  hooks  at  end  of  main  furnace  corner 10 

6  lower  hooks  in  front 30 

52  loops  for  above  to  go  over  buckstaves 156 

30  loops  to  connect  irons  across  vault 90 

687  =  2,900 

Buckstaves,  old  rails,  90  pounds  to  the  yard. 
9  for  each  side  of  main  furnace,  at  6£  feet ,  117 

5  for  both  sides  of  fire-box,  at  6£  feet 33 

2  long  at  rear  end  of  fire-box,  at  9  feet 18 

2  at  main  end  corners,  at  6  feet 12 

6  at  front  of  furnace,  at  5  feet 30 

2  light  ones  for  fire-door 6 

2  longitudinal  rails  under  vault  to  connect  irons 

from  each  side,  at  16  feet 32 

248  =  7,470 

Crate-bars,  24  of  inch  square,  4  feet  3  inches. 345 

Arcs,  levers,  and  chains  for  fire-door  and  charging-door.. . .  92 

Skimming-bar,  6  feet  long,  §  inch  by  2  inches 26 

Bolts  and  nuts  about  furnace 72 

Clamps  for  flue-slabs  and  brick  doors 54 

Chain  to  damper 14 

Total,  except  old  rails 3,503 

WBOUGHT-IBON  FOR  COBNEBS  OF  STACK. 

480  feet  of  |  inch  by  |  inch  iron  for  uprights 605 

360  feet  £  inch  by  1|  inch  iron  for  cross  straps 532 


Total 1,137 

RESUME  OF  IRON  WORK. 

Cast-iron,  6,855  pounds  at  2£  cents $171.36 

Wrought-iron,  4,640  pounds  at  2  cents 92.80 

Old  rails 56.03 

$320.20 


296     MODEKN  AMEEICAN  METHODS   OF  COPPER  SMELTING. 

LUMBER. 

Lumber  for  main  furnace  arch,  foundation    arch,  and 
chimney  scaffolding,  2,360  feet  at  $18 $42.48 

LABOR  ON  REVERBERATORY. 

Excepting  Foundations. 

Mason's  labor,  160  days  at  $4.00 ,  $640.00 

Helper's  labor,  165  days  at  $2.00 330.00 

Carpenter's  labor,  9  days  at  $3.00 27.00 

Blacksmith  and  helper's  labor,  8£  days  at  $5.00 42.50 

Ordinary  labor,  35  dajs  at  $1.50 52.50 

Grading  and  clearing  up 66.00 

Superintendence 124.00 

Incidentals 37.00 

Total  labor $1,319.00 

SUMMARY  OF  TOTALS. 

Excavation $49.50 

Stone- work 245. 00 

Fire-brick 840.00 

Dinas  brick 120.00 

Fire-clay 80.00 

Ordinary  clay 20.00 

Red  brick 424.00 

Lime,  sand,  and  cement 105.50 

Iron  work 320.20 

Lumber 42.48 

Labor,  superintendence,  etc 1,319.00 

Grand  total $3,565.68 

TOOLS. 

The  tools  for   a  reverberatory   smelting  furnace   should 
embrace : 

1  long  and  1  short  paddle. 

4  ordinary  skimming  rabbles. 
6  ordinary  stirring  rabbles. 

2  long  stirring  rabbles. 

2  long  clay  stampers  (for  repairing). 
2  short  clay  stampers  (for  repairing). 
4  steel  tapping-bars. 
1  striking  hammer. 


REVERBERATORY  FURNACES.  297 

1  sledge-hammer. 

4  steel  grating-bars,  assorted  lengths. 

1  coal  shovel. 

Ordinary  shovels. 

1  rake. 

1  iron  wheelbarrow. 

1  slag  barrow. 

Various  hooks,  pokers,  etc. 

Weighing  in  the  aggregate  (excepting  barrows,  shovels,  and 
such  tools),  iron,  about  1,300  pounds ;  steel,  about  275  pounds. 

All  rabbles  and  bars  are  made  and  repaired  at  the  furnace, 
the  heads  of  the  former  being  usually  imported  from  England, 
and  welded  on  to  the  wrought-iron  bar. 

ESTIMATE  OF  COST  OF  RUNNING  A  REVERBERATORY  FURNACE. 

It  is  assumed  that  coal,  ore,  and  fettling  materials  are  of 
good  average  quality,  and  that  the  cost  of  superintendence 
and  similar  expenses  is  divided  among  six  furnaces.  The 
helpers  of  neighboring  furnaces  assist  each  other  in  charging 
and  removing  slag. 

The  allowance  for  repairs,  as  well  as  all  the  figures  given, 
may  be  taken  as  reliable  under  the  conditions  assumed,  as 
they  are  the  average  results  of  a  year's  actual  work. 

The  cost  of  preparing  and  smelting  in  the  two  sand  bottoms 
is  also  given,  the  figures  adopted  being  the  average  of  nine 
such  operations,  and  consequently  including  such  mishaps  as 
will  occasionally  occur. 

The  general  expenses  of  the  works  are  too  variable  to  be 
properly  considered  in  such  an  estimate.  The  same  may  be 
said  regarding  fluxes. 

COST  OP  REVERBERATORY  FURNACE  BOTTOM. 

A — Lower  Bottom. 

Fire-sand  (or  prepared  quartz),  4 '75  tons  at  $8 $38.00 

Coal  for  preliminary  heating  and  fusion,  6*5  tons  at  $5. 

Two  smelters  at  $3  (24  hour's  operation) 

Two  helpers  at  $2 

One  laborer 

Proportion  of  coal  transportation 

Carried  forward. .  82.25 


298    MODERN"  AMERICAN   METHODS   OF   COPPER  SMELTING. 

Brought  forward $82.25 

Proportion  of  2  foremen  at  $4  each 1 . 33 

Lights,  oil,  soap,  etc .65 

Repairs  on  furnace  tools .60 

Clay  and  sand  for  doors,  tap-hole,  etc .15 

Total $84 . 98 

B — Upper  Bottom. 

Fire-sand  (or  prepared  quartz),  3 '9  tons  at  $8 $31.20 

Coal  for  sand-roasting  and  fusion,  5'2  tons  at  $5 26.00 

Two  smelters  at  $3 6.00 

Two  helpers  at  $2 •. 4.00 

Two  laborers  at  $1.50 3.00 

Transportation  of  slag  and  matte  to  soak  bottom .85 

Proportion  of  coal  transportation .20 

Proportion  of  2  foremen  at  $4  each 1 . 33 

Clay  and  sand  for  final  fettling,  doors,  tap-hole,  etc.  . .  1.60 

Lights,  oil,  soap,  etc .65 

Repairs  on  furnace  tools .75 

Total $85.58 

Grand  total $170 . 56 

COST  OP  RUNNING  REVERBERATORY  SMELTING  FURNACE  24  HOURS. 

Coal,  4*3  tons  bituminous  coal  at  $5 $21.50 

Clay  and  sand  for  fettling,  220  pounds .45 

Cheap  clay  and  loam  for  luting  ;  sand  for  matte  beds, 

800  pounds 60 

Proportion  of  renewing  upper  bottom  annually .24 

Proportion  of  renewing  main  arch  -annually .69 

Proportion  of  renewing  flue  quarterly .21 

Proportion  of  other  repairs  of  furnace .88 

For  renewing  tools  and  barrows 1 .36 

Repairs  on  tools  and  barrows 1 . 25 

Lights,  oil,  soap,  chalk,  etc .72 

Refuse  wood  for  drying  matte  beds  (only  happens  ex- 
ceptionally)   .12 

Repairs  on  furnace  doors .13 

Two  smelters  at  $3 6.00 

Two  helpers  at  $2 2.00 

One  laborer  (on  day  shift  only) 1 . 50 

Proportion  of  coal  transportation .25 

Proportion  of  ore  transportation .40 

Proportion  of  selecting  slag  and  building  dump 25 

Proportion  of  removing  ashes .25 

Proportion  of  2  foremen  (day  and  night)  at  $4  each 1 .33 

Allowance  for  extra  help  (exceptionally) .33 

$40.46 


REVERBERATORY  FURNACES.  299 

As  such  a  furnace  should  easily  smelt  12  tons  per  twenty- 
four  hours  of  favorable  ores,  the  cost  per  ton  would  be  $3.37, 
which  sum  will  be  augumented  by  a  certain  proportion  of  the 
general  expenses,  as  well  as  by  whatever  fluxes  may  be  found 
necessary  to  add. 

Where  iron  is  cheap,  the  entire  furnace  is  frequently  in- 
closed in  wrought  or  cast  plates  of  that  metal,  the  latter  being 
usually  seven-eighths  inch  thick  and  closely  perforated  with 
niche  holes,  coned  out  in  the  casting,  to  lessen  the  weight  of 
the  plates. 

"When  thus  supported,  the  exterior  red  brick  casing  may 
be  omitted,  as  well  as  the  massive  corners,  thus  giving  the 
main  body  of  the  furnace  a  coffin  shape.  This  is  the  case 
with  the  reverberatories  of  the  Orford  Copper  and  Sulphur 
Company  constructed  by  H.  M.  Howe. 

ORE  SMELTING  FOR  COARSE  METAL. 

This  operation  requires  the  highest  attainable  heat  in  the 
shortest  possible  time.  The  furnace,  therefore,  should  have 
a  comparatively  large  fire-box  and  flue,  and  also  a  hearth  of 
the  largest  practical  dimensions,  in  order  to  contain  a  suffi- 
cient charge  of  the  light  and  bulky  ore. 

Beginning  with  the  old  Swansea  standard  of  9  or  9J  feet 
width  of  hearth,  the  author  has  seen  this  gradually  enlarged 
to  11  feet,  without  increasing  the  size  of  the  fire-box  (3J  by  4 
feet)  or  the  consumption  of  fuel,  and  raising  the  capacity  of 
the  furnace  from  2  or  2J  tons  per  charge  to  3f  or  4J,  the  time 
of  fusion  in  both  cases  being  identical ;  that  is,  from  4$  to  7 
hours,  according  to  quality  of  fuel  and  fusibility  of  charge. 

Including  delays,  waste  of  time  in  charging,  tapping,  etc., 
4  charges  per  day  of  4  tons  each  may  be  considered  good 
average  work  for  calcined  ores  of  reasonable  fusibility,  and 
when  the  metal  produced  does  not  exceed  40  per  cent,  in 
copper.  The  production  of  a  richer  matte  lengthens  the  period 
of  fusion  for  several  reasons. 

Among  these  is  the  fact  that  rich  matte  does  not  possess 
the  power  belonging  to  low-grade  metal,  of  rapidly  floating  up 
and  detaching  the  semi-fused  masses  of  ore  from  the  furnace 


300     MODERN  AMERICAN  METHODS  OF  COPPEE  SMELTING. 

bottom,  and  thus  shortening  the  process.  Rich  matte  also 
presupposes  a  quite  thorough  calcination,  so  that  there  is  not 
only  a  less  proportion  of  easily  fusible  sulphides,  but  much  of 
the  sulphide  of  iron  present  has  been  changed  into  ferric,  in- 
stead of  ferrous,  oxide,  which  is  nearly  infusible,  and  must  be 
for  the  most  part  reduced  to  the  lower  oxide  before  it  can 
combine  with  silica. 

For  these  reasons,  and  more  especially  for  fear  of  produc- 
ing too  rich  a  slag,  the  Swansea  custom  has  forbidden  the  pro- 
duction of  a  matte  from  the  first  fusion  of  above  35  per  cent, 
copper.  The  presence  of  arsenic  and  antimony,  which  require 
for  their  removal  a  long  series  of  alternate  oxidations  and  re- 
ductions, also  has  favored  this  practice ;  but  with  our  purer 
and  richer  native  ores,  and  with  the  high  prices  of  fuel  and 
labor,  it  has  become  the  custom  to  produce  a  much  higher 
grade  of  matte  at  the  first  fusion. 

This  also  is  the  practice  in  Chili,  where  the  first  matte  ap- 
proaches 50  per  cent. 

Long  experience  in  the  practice  of  making  a  first  rich  matte 
has  resulted  in  divesting  it  of  many  imaginary  as  well  as  real 
disadvantages.  The  following  pages  will  show  to  what  an  ex- 
treme it  has  been  pushed,  where  local  conditions  combine  to 
render  it  advantageous. 

The  very  high  prices  of  labor  and  material  at  Butte,  Mon- 
tana, and  the  comparative  cheapness  of  high-grade  ores  of 
copper,  render  that  metal,  while  in  the  ore,  about  the  cheapest 
thing  there ;  so  that  it  is  much  more  profitable  to  sacrifice  a 
small  portion  of  copper  than  to  attempt  to  save  it  all  at  the 
expense  of  fuel  and  labor. 

Nor  need  the  loss  of  copper  in  the  slags  from  even  the 
highest  grade  metal  be  as  great  as  is  often  supposed. 

The  following  results  of  work  executed  at  the  furnaces  of 
the  Parrot  Copper  Company,  of  Butte,  Montana,  illustrate,  as 
has  been  said,  the  extreme  practice  of  this  kind.  The  assays 
were  made  by  the  company's  chemist,  Mr.  D.  P.  Murphy. 

Each  assay  represents  a  shipment  of  matte  of  from  15  to 
16  tons,  while  the  slag  samples  are  average  results  of  each 
charge,  which  could  be  extended  to  almost  any  desired 
Urn  it  N 


REVERBEEATORY  FURNACES. 


301 


Assay  of  matte. 
Per  cent,  copper. 

64-3  

Assay  of  slag. 
Per  cent,  copper. 
0'85 

Assay  of  matte. 
Per  cent,  copper. 

61-8 

Assay  of  slag. 
Per  cent,  copper. 

0-64 

62-7  

1-05 

63-6. 

0*87 

66-5     

0-92 

64-5 

0-82 

66-2  

1-10 

63-3 

0*76 

65-9.. 

0-67 

66-2.. 

..1-32 

One  of  the  great  secrets  of  rapid  fusion,  always  assuming 
that  the  flue  and  chimney  are  of  the  proper  size,  and  that  the 
firing  is  managed  with  skill  and  regularity,  is  the  absolute  ex- 
clusion of  all  currents  of  air  from  the  interior  of  the  furnace. 
The  chilling  effect  produced  by  even  the  slightest  crack  or 
orifice  in  the  brick-work  or  from  deficient  claying  up  of  the 
doors,  would  be  incredible  to  the  inexperienced.  The  front 
and  side  doors,  made  of  fire-brick,  inclosed  in  an  iron  frame, 
are  fitted  closely  to  the  sides  of  the  furnace  surrounding  the 
door  openings,  and  all  cracks  luted  with  plastic  clay.  As  the 
charge  is  usually  too  siliceous  already,  and  as  any  addition  of 
this  clay,  which  is  sure  to  fall  down  upon  and  become  mixed 
with  the  ore  charge,  at  the  side  door,  is  a  decided  detriment, 
the  smelter  irses  the  smallest  practicable  quantity  of  the  same. 
This  shrinks  on  drying,  permitting  the  ingress  of  air  cur- 
rents, which  may  have  a  most  serious  effect  in  retarding  the 
process. 

The  author  has  remedied  this  by  substituting  for  the  worth- 
less clay  the  raw  slimes  from  the  settling-pits,  where  concen- 
tration is  employed,  or  fine  screenings  from  the  roast-heaps 
where  the  former  material  cannot  be  procured- 

This  may  seem  a  small  item,  but  the  quantity  of  lute  used 
is  very  great,  as  may  be  inferred  from  the  fact  that  the  substi- 
tution of  the  concentration  slimes  for  clay  in  works  containing 
six  reverberatory  furnaces  effected  an  increased  production  of 
1,000  pounds  of  copper  monthly  at  no  expense,  but  with  the 
saving  of  some  $15  in  clay. 

As  the  gangue  of  copper  ore  is  usually  quartzose,  the 
reverberatory  smelter  is  seldom  troubled  with  too  basic  a 
charge. 

Where  this  occurs,  it  is  a  decided  evil ;  for  although  ex- 
tremely fusible,  it  rapidly  destroys  the  fettling  and  sand  bot- 
tom, and,  what  is  of  far  greater  importance,  produces  so  thin 
and  fluid  a  slag  that  its  removal  from  the  metal  by  skimming 


302     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING.  ' 

is  almost  impossible.  In  such  instances,  the  only  remedy  is 
to  allow  the  liquid  charge  -to  cool  until  the  slag  has  stiffened 
sufficiently  to  render  its  removal  less  difficult,  or  to  throw  a 
considerable  quantity  of  ashes  or  coke-dust  over  the  surface 
of  the  bath,  which  acts  in  the  same  way.  It  is  sometimes 
necessary,  after  skimming  the  priDcipal  portion  of  the  slag,  to 
allow  the  remainder  to  chill  until  it  becomes  so  thick  that,  on 
tapping,  it  will  remain  in  the  furnace,  while  the  more  fusible 
matte  is  run  into  the  ordinary  sand  molds.  This  is  a  mis- 
nomer, however,  as  sand  would  be  the  worst  possible  material 
for  the  construction  of  molds,  a  sandy  loam  being  the  proper 
substance,  and  being  dampened  only  sufficiently  to  render  its 
manipulation  feasible.  It  must  be  thoroughly  dried  before 
tapping,  to  avoid  explosions,  especially  when  coarse  metal 
(below  45  per  cent.),  which  is  peculiarly  liable  to  this  accident, 
is  being  made.  The  richer  grades  of  matte  may  be  run  into 
quite  damp  molds  with  impunity.  But  special  care  must  be 
taken  with  blister  copper,  which  is  more  explosive  even  than 
the  lower  grades  of  matte.  If  serious  boiling  of  the  liquid 
metal  in  the  molds  occurs,  indicating  a  probable  impending  ex- 
plosion, the  spot  should  be  at  once  covered  with  old  boards, 
which  should  always  be  held  in  readiness.  Any  outbreak  is 
controlled  by  dry  sand,  water  being  avoided  in  all  cases. 
Fortunately,  these  demonstrations  are  less  dangerous  than 
they  appear,  and  very  few  cases  of  explosion  are  so  serious  as 
to  prevent  the  attendants  from  remaining  in  the  building  and 
protecting  it  from  destruction  by  fire.  A  little  pluck  and 
plenty  of  dry  sand  will  nearly  always  suffice  to  prevent  any 
serious  results. 

After  the  removal  of  the  pigs  of  matte  from  the  molds 
the  furnace-helper,  assisted  by  a  second  man,  the  sand  should 
be  raked  over  with  an  iron  rake,  and  all  coarse  pieces  returned 
to  the  next  charge. 

The  pigs  of  slag  from  the  slag-bed  may  be  generally  thrown 
over  the  dump,  but  the  plate  slag  should  be  re- smelted  entire, 
and  every  pig  of  slag,  when  cool,  should  be  carefully  exam- 
ined for  prills. 

It  is  more  advantageous  to  charge  a  furnace  by  the  side 
door  than  by  the  means  of  a  hopper  above  the  roof,  as  the 


REVERBERATORY   FURNACES.  303 

proper  leveling  and  distribution  of  the  heavy  charges  now 
used  are  almost  impracticable  by  means  of  the  rabble,  while, 
when  charged  with  a  shovel,  every  pound  of  ore  can  be  thrown 
just  where  it  is  needed.  In  order  that  no  time  be  wasted,  the 
helpers  from  other  furnaces  assist  in  charging,  at  least  four 
men  being  required.  The  work  is  exceedingly  hot  and  labori- 
ous, as  the  entire  process  should  be  completed  in  from  ten  to 
fifteen  minutes,  to  avoid  waste  of  time  and  fuel. 

The  tapping  of  the  metal  should  occur  as  seldom  as  pos- 
sible, as  the  influence  of  the  molten  matte  upon  the  fresh 
charge  is  very  favorable,  and  prevents  that  persistent  adher- 
ence to  the  bottom  that  is  ^one  of  the  chief  causes  of 
delay. 

In  case  a  charge  should  adhere  in  this  manner,  it  is  usu- 
ally bette.r  to  skim  it  as  soon  as  a  few  hundredweight  of  clean 
slag  can  be  obtained.  If  the  direct  contact  of  the  flame  for 
half  an  hour  or  more  still  fails  to  raise  the  old  charge  entirely, 
the  work  should  not  be  unreasonably  delayed,  but  the  fresh 
charge  should  be  distributed  in  such  a  manner  as  to  leave 
bare  those  portions  that  adhere  most  closely,  and  which  will 
usually  be  loosened  by  this  double  period  of  firing. 

Those  portions  of  the  hearth  subject  to  the  most  excessive 
heat  and  wear,  such  as  the  Abridge  and  side  walls,  should  be 
thickly  covered  with  ore,  even  to  the  extent,  if  necessary,  of 
heaping  three-fourths  of  the  charge  upon  a  comparatively  lim- 
ited area,  if  such  practice  be  found  conducive  to  the  quickest 
fusion  and  greatest  capacity. 

In  charging  a  mixture  composed  of  various  ingredients,  the 
succession  in  which  they  are  thrown  upon  the  hearth  is  by  no 
means  a  matter  of  indifference.  With  a  mixture  of  calcined 
pyrites  (or  matte),  raw  quartzose  ore,  and  rich  slag  (a  very 
common  charge),  the  calcined  ore  should  be  thrown  upon  the 
hearth,  which  it  protects  by  its  want  of  conductivity;  the 
quartzose  ore  should  come  next ;  while  the  very  fusible  slag 
should  surmount  the  whole.  In  this  way,  want  of  conductivity 
of  the  calcined  ore  is  prevented  from  delaying  the  fusion,  as  it 
would  if  it  covered  any  of  the  other  substances,  and  is  made 
positively  useful  in  protecting  the  hearth. 

The  size  to  which  ore  should  be  crushed  for  reverberatory 


304     MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

smelting  depends  upon  its  fusibility  ;  very  quartzose  ore  being 
benefited  by  passing  a  4-mesh  screen,  while  basic  or  sulphide 
ore  may  be  of  almost  any  reasonable  size. 

Very  fine  crushing  should  be  avoided,  both  on  account  of 
excessive  formation  of  flue-dust  as  well  as  of  its  property  of 
becoming  so  compact  as  to  resist  the  highest  tempera- 
tures. 

After  fusing  any  calcined  ferruginous  material  for  several 
days,  the  hearth  will  be  found  covered  with  slimy  masses  of 
reduced  iron,  which,  to  a  certain  extent,  may  be  beneficial  as 
a  protection  to  the  bottom,  but  when  beyond  a  certain  limit, 
must  be  removed  by  persistent  firing,  assisted,  when  necessary, 
by  a  small  charge  of  raw  sulphurets,  which  will  rapidly  float 
up  and  dissolve  the  accretions.  Several  thousand  pounds  of 
metal  are  often  obtained  in  this  manner  from  an  apparently 
empty  furnace. 

Every  metallurgist  should  be  capable  of  personally  judging 
of  the  condition  of  his  furnace  bottom,  as  the  shrewd  smelter 
may  gain  great  credit  for  speedy  smelting  by  skimming  his 
charges  before  they  are  really  completed,  while  the  honest 
furnace-man  who  waits  until  his  hearth  is  clear  before  throw- 
ing the  new  charge  may  receive  undeserved  blame. 

The  amount  of  detail  connected  with  the  management  of  a 
reverberatory  smelting-furnace  is  almost  endless,  and  while  it 
may  be  an  easier  task  to  manage  a  reverberatory  than  a  blast- 
furnace, for  an  inexperienced  man,  it  is  an  infinitely  greater 
attainment  to  be  a  thoroughly  skillful  reverberatory  furnace- 
smelter  than  to  have  equal  skill  in  the  management  of  the 
blast-furnace. 

SMELTING  FOR  WHITE  METAL. 

As  the  production  of  the  higher  grades  of  matte,  of  which 
white  metal  (from  TO  to  75  per  cent.)  may  be  regarded  as  the 
type,  by  means  of  the  fusion  of  calcined  coarse  metal  with 
quartzose  ores,  presents  no  sufficient  differences  from  ore 
smelting  to  demand  especial  notice  in  this  very  brief  treat- 
ment of  the  subject,  the  older  process  of  concentrating  metal 
without  the  intervening  calcination  need  be  alone  considered 
under  this  head. 


REVERBEKATORY  FURNACES.  305 

This  process  is  termed  "  roasting  "  by  the  English  smelter, 
and  denotes  the  gradual  fusion  of  the  coarse  metal  in  large 
pigs,  on  the  hearth  of  a  reverberatory  furnace,  with  the  abun- 
dant admission  of  air. 

It  is  seldom  practiced  in  the  United  States  on  account  of 
its  extreme  slowness  and  consequent  great  consumption  of 
fuel  and  labor,  but  it  possesses  the  advantage  of  great  simplic- 
ity of  plant,  dispensing  as  it  does  with  the  entire  crushing  and 
calcining  paraphernalia. 

Despite  the  simplicity  of  the  process,  much  experience  is 
required  to  obtain  the  best  results,  as  the  exact  degree  of  tem- 
perature at  the  differing  stages  of  richness  of  the  product  has 
much  to  do  with  the  rapidity  of  the  concentration. 

Experience  has  taught  that  the  rapidity  of  this  concentra- 
tion stands  in  exact  proportion  to  the  richness  of  the  matte 
operated  upon.  The  explanation  of  this  is,  that  the  sulphur, 
which  is  almost  the  sole  foreign  constituent  of  the  richest 
matte,  is  very  easy  of  oxidation,  while  the  iron,  which  increases 
with  the  decrease  of  copper,  oxidizes  with  much  greater  diffi- 
culty. 

The  writer  has  given  much  attention  to  this  subject  in 
connection  with  futile  efforts  to  effect  what  M.  Manhes  has 
now  accomplished  with  his  Bessemerizing  process.  The  fol- 
lowing table  gives  the  result  in  per  cent,  of  product  of  his 
experiments,  which  extend  over  several  years,  many  of  them 
having  been  conducted  for  the  Orford  Copper  and  Sulphur 
Company,  while  in  its  employ.  They  were  made  merely  to 
determine  the  rapidity  with  which  the  grade  of  the  matte  in- 
creases by  the  ordinary  method,  and  without  any  attempt  at 
Bessemerizing. 

Great  care  was  taken  in  all  instances  to  insure  the  correct 
sampling  and  assaying  of  the  substances  under  consideration. 

It  will  be  understood  that  the  matte  was  charged  in  the 
shape  of  large  pigs  ;  melted  down  during  the  time  indicated  (in 
most  instances,  about  five  hours),  and  retained  in  a  molten  con- 
dition (in  both  stages  with  the  free  admission  of  air)  for  vary- 
ing periods,  samples  being  taken  from  time  to  time — after 
thorough  stirring — to  determine  the  progress  of  the  concen- 
tration. 

20 


306     MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 


TABLE  OF  MATTE     CONCENTRATION     BY    OXIDIZING     FUSION — PERCENTAGES 
OF   COPPER   IN   FRACTIONS   OMITTED. 


i 

§1 

- 

1 

When 
melted. 

1 

to 

J3 

1 
t- 

£ 

o 

00 

0 

1 

o 

S 

2 

1 
1 

to 

1 

00 

E 

0 

8 

S 

o 

ft 

e 

c5 

£ 

£ 
1 

2 

3 
0 
fi 

3 

V.' 

1 

O 

fi 

o 

E 

I 

00 

TP 

16 

16 
93 

17 
9,9 

16 

19 

20 

20 
95 

21 

22 

21 

97 

... 

... 

23 

97 

... 

... 

23 

i 

... 

... 

25 

29 

33 

41 
50 

58 

37 
45 
55 

41 
69 

69 

39 
47 
57 

61 

61 

41 
53 
59 
69 

... 

65 

41 
54 
61 

65 

.  .  . 

44 

58 
61 
67 

68 

. 

49 
64 

.  .  . 

.  .  . 

... 

63 
69 

74 

67 

73 

89 

73 

74 

70 

74 
84 

72 
78 
88 

77 

82 

75 
85 
94 

78 
89 

99' 

84 
94 

98 

80 

86 

89 

93 

98 

86 

94 

99 

99, 

96 

96 

98 

99 

99 

96 

98 

99 

THE    MAKING  OF    BLISTER  COPPER. 

This  very  beautiful  and  economical  operation  is  entirely  of 
English  origin,,  and  though  virtually  belonging  under  the  head 
of  "  Matte  Concentration,"  presents  so  many  important  pecu- 
liarities as  to  demand  separate  notice. 

The  furnace  used  for  this  purpose,  while  an  ordinary  rever- 
beratory,  as  regards  size  and  shape,  should  be  very  strongly 
ironed,  to  withstand  the  large  charges  used  in  our  modern 
practice,  while  its  bottom  should  be  smelted  in  with  peculiar 
care,  and  its  upper  layer  should  be  thoroughly  saturated  be- 
fore used  with  metal  of  the  same  grade  as  blister  copper  (from 
96  to  98  per  cent),  to  prevent  the  certain  annoyance  from  the 
rising  of  bits  of  the  poorer  matte  just  at  the  completion  of  the 
process,  and  the  consequent  adulteration  of  the  whole  charge 
of  blister,  which  will  require  still  further  oxidation  to  remove 
the  impurities.  The  lower  bottom  may  be  slightly  saturated 
with  lean  matte  to  save  expense. 

The  metal  is  charged  in  large  pigs,  the  total  weight  de- 
pending principally  upon  its  grade  ;  for  as  a  full  bed  of  blister 
copper  (from  6  to  10  tons)  is  usually  desired  as  most  economi- 
cal, it  is  evident  that  a  much  greater  weight  of  blue  metal  (62 


REVERBERATORY  FURNACES.  307 

per  cent.)  will  be  required  than  of  white  metal  (75  per  cent.) ; 
while  pimple  metal  (83  per  cent.)  and  regule  (88  per  cent.) 
will  lose  still  less  in  the  process. 

The  technical  names  just  enumerated  apply  to  various 
grades  of  matte,  each  of  which  has  certain  invariable  charac- 
teristics, which  distinguish  it  with  certainty.  The  percent- 
ages given  therewith  are  not  absolute,  but  are  subject  to  con- 
siderable variation,  the  writer  giving  such  average  figures  as  his 
own  experience  has  determined  for  him. 

As  both  economy  and  a  due  regard  for  the  furnace  bottom 
prevent  the  blister  charges  from  covering  too  long  periods  of 
time,  it  is  necessary  to  shorten  the  same  by  using  either  a  less 
weight  of  matte,  or  insisting  upon  a  higher  grade  at  the  out- 
set. 

The  latter  is  the  proper  choice,  as  a  small  charge  is  almost 
certain  to  injure  the  furnace  bottom  by  leaving  a  portion  of  it 
exposed  to  the  direct  heat  of  the  flame. 

The  most  advantageous  lengths  for  the  working  off  of  a 
blister  charge  must  depend  largely  upon  local  circumstances. 
From  twenty-four  to  thirty-six  hours  will  finish  a  full  charge 
(eight  tons)  of  rich  pimple  metal. 

A  similar  weight  of  white  metal  may  require  fifty  hours, 
which  is  quite  long  enough  for  the  safety  of  the  furnace,  though 
a  much  greater  length  of  time  often  elapses  without  harm. 

As  will  be  readily  seen,  it  is  impossible  to  work  off  a  charge 
of  blue  metal  within  the  prescribed  limit  of  time,  while  even 
white  metal  extends  the  period  most  unpleasantly.  It  is 
therefore  much  better  with  metal  of  low  quality  to  divide  the 
operation  into  two  stages — producing,  for  example,  pimple 
metal,  or  regule,  the  first  time,  and  bringing  it  up  to  blister 
copper  by  a  second  step.  In  this  way,  full  charges  can  be 
used  without  endangering  the  furnace,  and  many  advantages 
are  gained. 

It  is  not  well,  however,  to  alternate  the  operations  in  the 
manner  just  suggested ;  but  rather  to  keep  the  furnace  on  one 
grade  of  metal  until  a  large  amount  is  collected,  and  then  take 
up  the  blister  process  and  maintain  it  until  all  the  concentrated 
metal  is  disposed  of.  In  this  way,  the  evil  of  attempting  to 
make  blister  copper  on  a  bottom  saturated  with  poorer  matte 


808     MODEEN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

is  avoided ;  and  the  exact  amount  of  concentrated  metal  re- 
quired for  a  full  charge  of  blister  can  always  be  had. 

The  matter  may  be  pushed  a  step  farther,  by  using  a  sep- 
arate furnace  for  each  operation  and  positively  interdicting 
the  use  of  the  blister  furnace  for  any  other  purpose. 

The  operation  of  making  blister  copper  is  frequently  exe- 
cuted by  constantly  maintaining  the  charge  in  a  molten  condi- 
tion after  it  is  once  melted,  and  never  allowing  it  to  chill  or 
"  set,"  as  it  is  technically  termed. 

By  pursuing  the  latter  plan,  however,  the  danger  to  the 
hearth  in  long  campaigns  is  greatly  lessened,  as  it  thus  has  a 
slight  opportunity  to  cool,  while  the  process  is  certainly  ad- 
vanced in  a  remarkable  degree  by  the  alternate  fusions  and 
chillings. 

The  belief  that  the  operation  of  tapping  causes  a  great  gain 
in  the  grade  of  the  matte,  expressed  among  the  Welsh  smelt- 
ers by  the  vulgar  saying  that  "  two  tappings  is  worth  one 
blowing,"  is  contradicted  by  the  following  experiments  exe- 
cuted by  the  writer  for  the  purpose  of  determining  the  truth  or 
falsity  of  the  common  belief : 

After 
tapping. 
Per  cent. 

No.  1  Copper 53-2 

No.  2  Copper 68'0 

No.  3  Copper 70*2 

No.  4  Copper 75'2 

No.  5  Copper 79*1 

No.  6  Copper 86  '2 

No.  7  Copper 93'2 

No.  8  Copper 98*5 

Average 623  -6 


Just  before 
tapping. 
Per  cent. 

No.  1  Copper 53'6 

No.  2  Copper 66'8 

No.  3  Copper 72'7 

No.  4  Copper 75-4 

No.  5  Copper 79*3 

No.  6  Copper 85'4 

No.  7  Copper 94'0 

No.  8  Copper 98'7 


Average 625' 


A  few  test  assays  that  showed  a  remarkable  variation  one 
way  or  the  other  were  discarded,  and,  as  seen,  the  others  ac- 
tually show  an  average  lower,  rather  than  higher,  grade  of  the 
metal  after  tapping,  which  is  doubtless  merely  an  accidental 
circumstance. 

The  exact  grade  at  which  the  blister  copper  should  be 
tapped  is  a  matter  of  much  importance,  as  both  too  high  and 
too  low  a  copper  presents  physical  qualities  injurious  to  the 
requirements  of  the  process. 


REVERBERATORY  FURNACES.  309 

Blister  copper  of  just  the  right  grade  is  highly  "  red-short ; " 
that  is,  can  be  easily  broken  when  red-hot.  It  is  this  quality 
that  enables  the  furnace-man  to  break  and  separate  his  pigs 
of  blister  copper,  which  operation  is  rendered  greatly  more 
difficult  by  a  very  slight  variation  in  percentage  in  either  di- 
rection. The  proper  condition  of  the  charge  is  easily  made 
manifest  to  the  experienced  by  ocular  inspection,  and  the 
writer  has  endeavored  to  fix  the  limits  that  bound  the  grade 
of  copper  possessing  this  important  quality. 

Foreign  impurities  exert  so  much  influence  in  this  direction 
as  to  render  impossible  any  exact  establishment  of  such  bound- 
aries ;  but  numerous  tests  have  fixed  the  most  favorable  grade 
between  96J  and  99  per  cent. 

An  important  precaution  in  the  care  of  a  blister  furnace  is 
the  proper  draining  of  the  hearth  and  stopping  of  the  tap-hole. 
Carelessness  in  this  respect  will  permit  a  slight  and  unsus- 
pected leakage  during  the  entire  period  of  blister-making,  cul- 
minating in  a  mass  of  metallic  copper  filling  the  entire  tap- 
hole,  and,  as  has  occurred  to  the  writer,  requiring  the  combined 
efforts  of  the  furnace  personnel  and  blacksmith  employes  for 
twelve  hours  to  remove  it. 

The  charge  being  high  blister,  and  just  ready  to  tap,  exerts 
a  ruinous  effect  upon  the  furnace  bottom  during  any  such  de- 
lay, and  should  be  ladled  out  at  once  under  similar  circum- 
stances. 

The  slag  from  the  blister  process,  being  very  rich  in  oxide 
of  copper,  should  be  returned  to  some  process  where  the  pro- 
duct is  of  high  grade,  and  not,  as  is  often  the  case  in  this 
country,  sent  back  to  the  ore  smelting,  where  its  copper  con- 
tents are  thrown  back  again  to  the  condition  of  a  base  sul- 
phide. 

The  following  are  examples  of  the  composition  of  the  slag 
and  copper  produced  by  this  roasting-smelting  for  blister  cop 
per,  taken  from  Mr.  Howe's  paper  already  referred  to  : 


310     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 


o* 

s  SP 

•%« 

1 

"Roaster"  slags 
from  Kaafiord.t 

Welsh  blistered 
copper. 

SH 

2    • 

n 

°«d 

*a  si 

£M 

l| 
5£ 

Silica                               

47-5 

86-0 

Copper  

99-2-99-4 

Protoxide  of  iron 

28'0 

7-0 

Iron  

-•7-0-8 

0-1-  0*2 

8-0 

6-0 

Nickel  and  cobalt. 

0-3-0-9 

0-2-  0'3 

Dinoxide  of  copper   CuaO 

16'9 

43-2 

Zinc   

O-Q-  0'02 

2-7 

Tin  

0-6-6-7 

Masrnesia               

0-8 

Arsenic  

0-4-1-8 

Nickel  and  cobalt  oxides 

0  9 

4-9 

Sulphur    

O'l-G-9 

0-1-  0'12 

Oxide  of  tin  

03 

0-6 

Oxide  of  zinc    

9-0 

3-2 

COPPER    REFINING. 

'  The  only  method  of  copper  refining  practiced  in  the  United 
States,  or,  in  fact,  in  the  civilized  world,  is  the  ordinary  Swan- 
sea process.^ 

The  purity  of  our  local  ores  and  the  simplicity  of  our  trade 
requirements  have  prevented  the  development  of  those  marked 
variations  that  characterize  the  English  process,  where  "  best 
selected,"  "  tough  cake,"  "  founder's  metal,"  and  many  other 
distinct  varieties  are  demanded  and  produced. 

The  great  excellency  of  the  Lake  Superior  copper,  derived 
from  pure  metallic  ores,  has  established  a  very  high  standard 
in  our  markets,  and  owing  to  the  abundant  supply  of  the  same, 
manufacturers  have  not,  until  recently,  found  it  necessary  to 
study  the  behavior  or  familiarize  themselves  with  the  capabil- 
ities of  other  brands  of  copper  for  certain  uses,  but,  feeling 
sure  that  if  they  bought  the  best  they  would  be  safe,  have 
employed  this  unnecessarily  superior  metal  for  the  manufac- 
ture of  brass  castings,  and  many  other  purposes  where  a 
poorer  quality  would  have  served  equally  well. 

The  most  impure  domestic  coppers  are  often  sufficiently 
argentiferous  to  repay  a  separate  process  by  which  the  quality 
of  the  baser  metal  is  improved,  while  the  nobler  is  saved — of 
late  largely  by  electrolytic  means. 


*  Le  Play,  op.  cit.,  p.  218.   f  Kerl,  Grundriss  der  Metallhuttenkunde,  i.,  p.  215. 
\  A  few  unimportant  exceptions  to  this  statement  may  still  exist. 


REVERBERATORY  FURNACES.  311 

Though  the  details  of  the  refining  process  have  been  stud- 
ied with  great  care  by  various  authors — among  whom  our  own 
Egleston  is  distinguished  by  the  exactness  and  extent  of  his 
investigations — any  practical  description  of  the  same,  from 
the  stand-point  of  the  working  refiner,  is  wanting.  The  fol- 
lowing brief  review  is  offered  as  a  slight  contribution  in  that 
direction. 

The  refining-furnace  presents  no  peculiarities  to  distin- 
guish it  from  the  ordinary  English  reverberatory,  except  that 
it  should  be  more  strongly  constructed ;  being  provided  with 
a  massive  front  plate — below  the  skimming-door — as  well  as 
strong  horizontal,  lateral  braces  to  strengthen  the  hearth, 
which,  in  addition  to  the  enormous  expansive  force  caused  by 
the  high  temperature,  must  also  sustain  the  weight  of  from  10 
to  15  tons  of  molten  metal. 

The  ash-pit  is  very  advantageously  provided  with  iron 
doors,  which  may  be  closed  during  the  ladling,  to  exclude  all 
currents  of  air,  while  the  flue  is  brought  as  nearly  as  possible 
over  the  skimming-door,  in  order  that  the  air-current  that 
enters  therefrom  may  ascend  at  once  without  affecting  the 
metallic  bath.  A 

The  two  bottoms  are  smelted  in  with  unusual  care,  and 
the  upper  one  thoroughly  saturated  with  repeated  small 
charges  of  metallic  copper.  This  should  be  spread  over  the 
entire  surface  in  the  shape  of  granules,  and  should  be  rapidly 
fused  until  it  is  entirely  liquid.  At  first,  nearly  all  will  be 
absorbed,  but  eventually,  a  larger  and  larger  proportion  will 
be  regained,  and  thoroughly  dipped  from  the  ladling-hole  at 
the  close  of  each  operation.  A  hearth  of  the  ordinary  size, 
9  J  by  14  feet,  will  absorb  from  6,000  to  18,000  pounds  of  copper 
during  the  "  soaking  "  process,  according  to  the  quality  of  the 
sand  and  the  temperature  attained  during  the  "  smelting  in  " 
of  the  bottom. 

On  no  account  should  metal  of  poor  quality  be  used  for 
purposes  of  saturation.  This  is  a  fatal  economy,  as  the  grade 
of  ah1  copper  refined  in  the  furnace  for  many  months  will  be 
affected  thereby. 

Even  after  the  bottom  is  well  saturated  and  has  attained  a 
considerable  degree  of  firmness,  the  careful  refiner  will  avoid 


312     MODERN  AMERICAN  METHODS  OF  COPPER  SMELTING. 

any  possible  injury  thereto  from  heavy  masses  of  metal.  It  is 
not  uncommon  to  charge  pigs  of  blister  copper  weighing  1,000 
pounds  or  more,  the  sharp  corners  and  edges  of  which  are 
very  liable  to  cause  indentations  and  unevenness  in  the  tough- 
est bottom,  which  may  serve  as  the  starting-point  for  serious 
after-effects.  All  such  injuries  may  be  avoided  by  laying 
down  a  rough  floor  of  old  planks  or  similar  material. 

The  fuel  best  suited  to  refining  is  a  not  too  caking  bitumi- 
nous coal  with  long  flame.  Sulphur-bearing  coals  should  be 
avoided,  as  tending  to  alter  the  "pitch  "  of  the  metal  at  criti- 
cal moments.  Where  such  coal  is  expensive,  a  cheaper  variety 
may  be  used  for  the  earlier  stages  of  the  process. 

No  better  fuel  exists  for  refining  than  wood,  as  its  freedom 
from  sulphur  and  other  impurities,  and  the  long,  pure,  non- 
reducing  flame  that  it  yields,  peculiarly  fit  it  for  the  purpose. 
It  was  used  entirely  at  the  Ore  Knob  Eefining- Works  with 
great  satisfaction,  and  would  be  more  frequently  employed 
were  it  cheaper  at  the  great  copper  centers. 

The  capacity  of  a  refining-furnace  should  be  increased  by 
deepening  the  hearth  rather  than  enlarging  its  area,  as  the 
difficulty  of  retaining  the  copper  in  proper  pitch  is  greatly 
heightened  by  increasing  the  surface  area.  Within  certain 
limits,  this  may  be  effected  by  constructing  a  clay  dam  at  the 
skimming-door ;  beyond  this,  the  deepening  must  be  effected 
by  lowering  the  bottom,  which,  in  any  case,  must  pitch  toward 
the  ladle-hole  from  every  point. 

The  size  of  the  charge  is  limited  rather  by  custom  and  the 
capacity  of  the  attendants  than  by  the  size  of  the  furnace,  and 
has  been  greatly  increased  of  late  years. 

During  the  writer's  student  years  a  charge  of  14,000  pounds 
was  considered  large,  but  the  present  English  refiners  vary 
from  18,000  to  25,000  pounds.  One  of  the  French  metallur- 
gists at  the  Exhibition  told  me  25,000  pounds  was  then  the 
standard  in  France. 

The  Lake  Superior  refineries  are  charged  with  some  18,000 
pounds  of  80  per  cent.  "  mineral,"  producing  over  14,000 
pounds  of  pure  copper.  This  may  be  regarded  as  an  average 
quantity,  but  the  Orford  Company,  ever  foremost  in  increase  of 
capacity,  has  found  no  difficulty  in  refining  charges  of  even 


REVERBERATORY   FURNACES. 


313 


314     MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

30,000  pounds.  The  principal  trouble  with  large  charges  is 
the  tendency  of  the  refined  copper  to  get  "  out  of  pitch,"  when 
retained  in  a  molten  condition  for  so  long  a  time  that  fresh 
coal  must  be  several  times  thrown  upon  the  grate.  Another 
difficulty  is  the  want  of  room  between  hearth  and  roof  to  ac- 
commodate such  a  weight  of  metal.  The  shape  and  irregular- 
ity of  the  pigs  of  blister  copper,  and  the  difficulty  of  accu- 
rately placing  such  awkward  bodies  in  the  desired  position  in 
a  red-hot  furnace,  have  also  prevented  the  ordinary  use  of 
larger  charges.  This  is  remedied  in  the  Lake  furnaces  by  less- 
ening the  customary  pitch  of  the  roof  from  bridge  to  charg- 
ing-door,  and  curving  it  down  abruptly  at  the  latter  point. 

Great  care  must  be  observed  regarding  the  quality  of  all 
material  allowed  to  enter  the  refining-furnace.  It  is  not  an 
apparatus  for  the  concentration  of  matte,  but  simply  to  alter 
the  shape  of  metal  that  is  already  nearly  pure,  and  to  put  the 
finishing  touches  on  it.  Much  of  the  pig-copper  produced 
from  blast-furnace  work  from  both  carbonate  and  sulphide 
ores  may  advantageously  undergo  a  preliminary  purifying  pro- 
cess in  the  blister  furnace.  All  copper  below  96  per  cent, 
should  be  thus  treated  ;  a  mere  melting  down  with  free  admis- 
sion of  air  being  sufficient  to  produce  a  99  per  cent,  blister 
copper  in  most  cases,  so  that  two  charges  of  16,000  pounds 
each  can  be  thus  treated  in  twenty-four  hours. 

A  few  hundred  pounds  of  the  richest  refinery  slag  from  the 
last  skimming  may  be  returned  to  the  same  operation,  the  rest 
going  back  to  the  last  preceding  operation. 

Cement  copper  from  wet  processes  should,  ill  most  cases, 
be  treated  in  the  blister  furnace.  It  must  be  thoroughly  damp- 
ened to  prevent  mechanical  loss,  and  when  mixed  with  white 
metal  to  the  extent  of  one-fourth  or  one-third  of  the  entire 
charge,  assists  so  materially  in  enriching  the  product  and  in 
shortening  the  operation,  that  it  just  about  repays  the  cost  of 
its  treatment. 

Mr.  James  Douglas,  Jr.,  has  regularly  produced  such  pure 
cement,  from  both  the  old  and  new  Hunt  &  Douglas  process, 
that  it  is  refined  at  once  with  advantage.  The  principal  draw- 
back is  its  excessive  bulk,  which  renders  it  necessary  to  add 
the  cement  in  several  successive  portions,  to  obtain  a  full 


REVERBERATORY  FURNACES. 


315 


316     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

charge.  This  may  be  obviated  by  pressing  it  into  bricks 
while  yet  damp. 

But  one  charge  can  be  treated  in  a  refining-furnace  each 
twenty-four  hours,  and  in  ordinary  cases,  the  labor  connected 
therewith  consists  of  one  head  refiner,  three  or  four  ladlers  (ac- 
cording to  whether  the  refiner  acts  also  as  ladler),  one  night 
refiner,  one  man  to  lift  the  ingots  from  the  boshes,  one  to  dump 
the  molds,  and  one  to  remove  any  accidental  impurities  from 
the  ladles,  dry  the  molds,  etc.  The  latter  three  operations  are 
often  conducted  by  boys.  One  man  is  also  required  to  re- 
move the  ingots  to  the  packing-house,  while  the  packing  itself, 
and  the  transportation  and  manipulation  of  the  new  charge, 
are  effected  by  the  furnace  personnel,  which  usually  expects  to 
conclude  the  day's  labor  by  three  P.M.  The  work  is  very  hot 
and  severe  while  it  lasts,  and  in  the  cases  of  the  large  charges 
referred  to,  extra  assistance  may  be  required  for  packing  the 
copper  and  similar  extraneous  work. 

While  the  quality  of  the  copper  depends  largely  upon  the 
skill  of  the  refiner,  its  external  appearance  and  neatness  are 
principally  influenced  by  the  ladlers.  As  these  latter  qualities 
exercise  an  undue  influence  upon  the  sale  of  copper  in  this 
country,  it  is  of  great  importance  to  create  a  body  of  trained 
and  skillful  workmen,  whose  pride,  as  well  as  self-interest,  is 
enlisted  in  the  matter. 

The  color  of  the  copper  has  an  influence  with  American 
buyers  entirely  disproportionate  to  its  importance  as  a  sign  of 
purity.  A  deep  rose-red  is  the  color  most  prized,  while  any 
brassy  appearance  is  very  damaging  in  the  eye  of  the  buyer. 

As  this  dirty  yellow  appearance  can  be  produced  at  pleasure 
by  allowing  the  copper  to  remain  a  few  seconds  too  long  in  the 
molds  before  it  is  dumped  into  water,  while  the  poorest  copper 
may  be  colored  a  fine,  deep  red  by  lifting  it  out  of  the  water 
for  a  second  immediately  after  dumping,  and  then  returning  it 
again  to  the  trough,  as  well  as  by  the  use  of  innumerable  baths 
or  "  pickles,"  it  certainly  should  not  be  regarded  as  of  such 
vital  importance.  It  is  true,  nevertheless,  that  pure  coppers 
take  on  the  desired  color  with  much  greater  ease  than  those 
containing  arsenic,  antimony,  or  various  other  substances,  and 
in  the  case  of  the  remarkably  pure  Lake  Superior  metal,  it  is 


REVERBERATOKY  FURNACES. 


317 


318      MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

very  difficult  to  produce  that  dreaded  brassy  appearance  which 
any  impurity  of  water  or  want  of  care  is  certain  to  develop  in 
ordinary  cases. 

The  red  color  is  produced  by  the  formation  of  a  minute  film 
of  suboxide  of  copper ;  but  why  this  hue  should  be  affected 
by  slightly  brackish  water,  or  by  changes  of  temperature  in  the 
cooling  water,  it  is  difficult  to  understand.  Pure  water  should 
be  used  and  the  most  favorable  temperature  discovered  for 
each  variety  of  copper.  In  some  cases,  it  must  be  nearly  boil- 
ing ;  in  others,  stone-cold ;  while  in  still  other  instances,  the 
refiner  corrects  an  unfavorable  coloring  by  the  introduction  into 
the  cooling-boshes  of  soda-ash,  salt,  saw-dust,  coal  ashes,  and 
various  other  apparently  inactive  substances. 

The  refin ing-furnace  usually  receives  its  fresh  charge  imme- 
diately after  it  has  been  emptied  of  the  preceding  one.  The 
fire  is  not  urged  until  evening,  in  order  that  the  first  two  stages 
of  the  operation,  the  fusion  and  the  fining,  may  not  be  com- 
pleted before  the  day  shift  comes  on  to  execute  the  refining 
proper — the  third  and  final  stage. 

With  pig-copper  of  reasonably  good  quality,  the  process  of 
fusion  may  be  begun  at  seven  or  eight  P.M.,  and  be  pushed  as 
rapidly  as  possible.  Owing  to  the  high  heat-conducting  qual- 
ity of  this  metal,  the  pigs  retain  their  shape  until  the  fusing- 
point  is  reached,  when  they  soften  and  melt  almost  instantane- 
ously. From  the  reducing  character  of  the  flame,  only  slight 
chemical  changes  have  thus  far  been  produced ;  but  as  soon  as 
the  protecting  layer  of  slag  is  removed  from  the  surface  of  the 
bath,  and  air  freely  admitted,  the  process  of  purification  pro- 
ceeds with  great  rapidity,  both  from  the  direct  oxidation  of  the 
foreign  substances  present,  as  well  as  by  the  more  far-reaching 
and  powerful  reaction  of  oxide  of  copper  upon  all  those  metal- 
loids and  bases  that  have  a  greater  affinity  for  oxygen  than 
the  copper  itself.  A  thin  slag  forms  rapidly  upon  the  surface, 
and  is  removed  at  intervals  of  an  hour  or  so.  The  constant 
escape  of  anhydrous  sulphuric  acid  causes  a  persistent  ebulli- 
tion, which  tends  greatly  to  facilitate  the  process  of  oxidation. 
As  the  proportion  of  base  metals  becomes  diminished,  the  slag 
is  more  strongly  colored  with  the  red  oxide  of  copper,  until  that 
produced  toward  the  close  of  this  stage  contains  from  40  to  70 


EEVEKBERATORY  FURNACES. 


319 


a  Fireplace. 
6   Ash-pit. 
c   Bridge  wall. 

d   Air  passage  controlled  by  valve  e, 
e   Bridge  valve. 

/  Air  passage  controlled  by  the  valve  g, 
g  Roof  valve. 

h   Laboratory  of  the  furnace. 
i   Hearth  of  sand  &  copper. 
J   Arch  supporting  the  hearth. 
k   Charging  door. 
I   Working  door. 
m   Fire  door. 
n    Chimney  68  feet  high. 
o   Flue  to  n. 
q   Movable  roof. 

«   Cast  Iron  T  bars  holding  furnace  together. 
t   Air  passages  leading  to  d. 
u    Socket  for  bars  v  and  w. 
v   Ear  for  the  repair  epodeL 
v>   Pole  bar. 
x   Bar  of  movable  roof . 


6018845  10  15  Ft. 

KEVERBERATOKY   FURNACE  AT  THE  LAKE   SUPERIOR  SMELTING-WORK8.—  REAR  ELEVATION. 


320     MODEEN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

per  cent,  of  this  metal,  and  becomes  a  valuable  oxidizing  flux 
for  the  preceding  blister  process.  The  total  amount  of  slag 
produced  during  the  operation  of  refining  depends  principally 
upon  the  quality  of  the  pig-copper,  but  is  seldom  less  than  12 
per  cent,  of  the  entire  charge,  containing  from  4  to  6  per  cent, 
of  the  total  weight  of  copper. 

The  gradual  cessation  of  ebullition  and  the  rapid  formation 
of  oxide  of  copper  by  no  means  indicate  the  entire  disappear- 
ance of  the  sulphur  present,  which,  from  its  strong  affinity  to 
copper,  remains  dissolved  in  the  bath  with  great  tenacity.  If 
the  oxidizing  process  has  been  sufficiently  thorough  to  insure 
the  presence  in  the  liquid  metal  of  a  perceptible  quantity  of 
suboxide  of  copper  (from  0*2  to  O7  per  cent,  according  to  dif- 
ferent authorities),  a  small  sample  ingot  poured  at  this  stage 
will  exhibit  a  very  peculiar  and  characteristic  phenomenon. 
On  cooling,  it  will  suddenly  rise  in  a  line  along  the  center, 
often  forming  an  abrupt  ridge  several  lines  in  height,  and  having 
an  irregular  and  granular  fracture.  This  is  said  to  be  due  to 
the  absorption  of  sulphurous  acid,  a  property  only  possessed 
by  metal  containing  a  considerable  proportion  of  suboxide  of 
copper,  but  still  unrefined  and  tenaciously  holding  on  to  a 
trace  of  sulphur  and  other  impurities.  The  process  of  "  flap- 
ping "  or  "  rabbling  "  is  now  begun,  by  which  the  liquid  bath, 
through  the  side  door,  is  constantly  agitated  in  a  peculiar 
manner  by  means  of  a  small  rabble. 

It  is,  of  course,  a  purely  oxidizing  operation,  and  both  te- 
dious and  slow,  requiring,  on  an  average,  two  hours  of  constant 
work.  Although  seemingly  a  most  awkward  and  ineffectual 
means  of  agitating  an  extensive  bath  of  molten  metal,  and 
bringing  all  its  particles  in  contact  with  the  atmospheric  air, 
it  has  never  been  improved  upon.  The  copper  now  becomes 
"  dry  "  from  the  dissolved  suboxide,  and  when  poured  into  a 
mold,  sets  with  a  deep  depression  upon  its  surface,  while  its 
fracture  has  a  characteristic  mottled  appearance,  following  upon 
a  previous  fine-grained  surface,  as  particularly  mentioned  by 
Professor  Egleston  in  his  valuable  paper  on  "  Copper  Kefining 
in  the  United  States."  The  color  is  a  brick-red,  but  both 
grain  and  color  are  so  influenced  by  the  temperature  at  which 
the  metal  is  poured,  as  well  as  by  the  rate  of  cooling  as  deter- 


REVERBERATORY  FURNACES. 


321 


322     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

mined  by  the  size  of  the  test-ingot,  that  these  signs  must 
always  be  taken  in  conjunction  with  other  and  more  reliable 
indications.  The  metal  during  this  period  is  undergoing  a 
powerful  scorification  from  the  dissolved  oxide  of  copper,  and 
most  injurious  impurities  are  gradually  oxidized,  and  either 
effectually  removed  by  slagging  or  volatilization.  Certain 
metalloids,  however,  resist  this  scorifying  influence  to  a  re- 
markable degree,  and  consequently  have  a  most  injurious  effect 
upon  the  refined  metal.  These  are  arsenic,  antimony,  and 
tellurium,  mentioned  in  the  order  of  their  harmfulness.  The 
extreme  importance  of  the  subject  warrants  the  mentioning  of 
the  best  means  to  remove  the  two  first-mentioned  impurities, 
the  latter  having  come  but  once  within  the  author's  experi- 
ence, and  probably  requiring  the  employment  of  one  of  the 
electric  or  chemical  methods,  by  which  excellent  copper  can  be 
made  from  very  poor  material. 

A  careful  trial  of  Vivian's  invention  of  dry-sweating,  by 
which  the  impure  blister  copper  is  exposed  to  a  long  oxidiz- 
ing heating  just  below  the  fusion-point,  has  not  succeeded 
with  the  writer ;  but  the  addition  of  from  3  to  5  per  cent,  of 
pure  white  metal — subsulphide  of  copper — to  the  bath  at  the 
beginning  of  the  refining  process  (as  suggested  by  some  person 
forgotten  by  the  author)  has  a  most  rapid  and  satisfactory 
effect  in  removing  both  arsenic  and  antimony.  Very  bad  cases 
may  require  two  such  additions,  with  an  intervening  oxidizing 
operation.  A  still  more  sure  and  radical  method  consists  in 
exposing  the  arsenical  ore  to  a  dead  roast,  and  subsequently 
smelting  the  same  with  a  large  proportion  of  iron  pyrites — cu- 
priferous, if  possible.  The  resulting  low-grade  matte  should 
be  regarded  and  treated  as  a  sulphide  ore,  and  will,  if  the  ini- 
tial calcination  is  thoroughly  conducted,  be  free  from  either 
arsenic  or  antimony.  * 

The  process  of  reduction  follows  that  of  oxidation,  and  the 
suboxide  of  copper,  having  served  its  purpose  as  a  purifying 

*  The  author  is  unable  to  give  the  original  sources  of  many  statements  here 
made  and  tested  by  himself  with  satisfaction,  and  desires  to  distinctly  dis- 
claim any  originality  in  any  operation  or  apparatus  pertaining  to  copper  met- 
allurgy ;  having  always  preferred  to  adopt  those  improvements  that  have 
been  thoroughly  tested  by  others  of  a  more  original  turn  of  mind. 


REVERBERATORY  FURNACES.  323 

agent,  must  now  be  reduced  to  metal  again ;  otherwise,  the 
copper  would  be  brittle  both  when  cold  or  at  higher  tempera- 
tures, and  unfit  for  manufacturing  purposes.  The  reduction  is 
effected  by  means  of  a  long  pole,  as  large  as  can  be  introduced 
into  the  furnace  and  of  any  kind  of  green  wood — hard  wood 
being  the  most  economical.  This  being  buried  in  the  metal 
bath,  evolves  an  immense  volume  of  hydrocarbons  and  other 
reducing  gases,  and  rapidly  removes  the  excess  of  oxygen.  The 
surface  of  the  metal  is  also  covered  with  charcoal,  to  prevent 
access  of  air,  and  samples  are  constantly  taken  to  determine 
the  condition  of  the  copper.  The  entire  removal  of  all  the 
oxygen  present  is  impossible,  even  over-poled  copper,  ac- 
cording to  Egleston,  *  containing  over  0*1  per  cent  of  oxygen. 
An  otherwise  tough  copper  may  become  brittle  from  over-poling, 
and  this  is  doubtless  due  to  the  fact  that  the  impurities  that 
were  present  in  the  tough  copper  were  dissolved  as  oxides  and 
consequently  innocuous,  but  on  being  reduced  to  the  metallic 
state,  at  once  asserted  their  deleterious  influence. 

The  poling  usually  lasts  an  hour  or  more,  and  is  continued 
until  a  full-sized  test-ingot  shows  no  contraction  or  depression 
on  cooling,  and  the  texture  is  extremely  fibrous  and  silky,  and 
of  a  beautiful  rose-red.  Further  tests  are  made  by  nicking  and 
bending  test  bars,  and  by  hammering  out  a  piece  into  a  thin 
plate,  which  should  show  no  cracks  at  the  edge.  This  condition 
of  tough-pitch  is  essential  to  copper  used  for  rolling  or  wire 
drawing,  but  is  entirely  superfluous  for  ingot  copper  that  is  to 
be  used  for  brass  founding  ;  as  it  may  be  easily  imagined  that 
the  fusion  that  it  undergoes  in  the  brass-founder's  crucible, 
under  various  oxidizing  and  reducing  influences,  effectually 
upsets  the  exquisite  niceties  of  the  refining  process,  so  far  as 
the  proportion  of  dissolved  suboxide  is  concerned. 

A  volume  could  be  easily  filled  with  practical  comments 
upon  the  process  of  refining,  but  space  forbids  any  further  de- 
tails. The  addition  of  lead  to  copper  intended  for  rolling  is 
quite  common  in  England,  and  is  doubtless  beneficial  with 
many  impure  coppers.  The  purer  copper  of  the  Lake  District 
and  from  the  Arizona  carbonates  does  not  seem  to  receive  any 
benefit  from  this  practice. 

*  See  Copper  defining  at  Lake  Superior  by  T.  Egleston. 


324      MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

The  molds  used  for  the  casting  of  ingots  should  always  be 
made  of  copper,  and  are  easily  and  rapidly  produced  by  the 
ordinary  ingot  stamp,  as  illustrated  in  Egleston's  paper.  The 
proper  taper  of  the  mold  and  the  proportion  of  surface  in  con- 
tact with  the  ingot  have  an  important  effect  upon  the  ease  with 
which  the  mold  delivers.  When  the  copper  is  ladled  too  hot, 
the  molds  are  rapidly  ruined,  and  as  at  best  they  wear  rapidly, 
they  should  be  returned  to  the  refining-furnace  as  fast  as  they 
become  in  the  least  imperfect ;  otherwise,  constant  annoyance 
and  accidents  will  result  from  the  obstinate  sticking  of  the 
ingots. 

The  ladles  used  in  the  refining  process  come  almost  exclu- 
sively from  England,  and  are  made  of  a  peculiar  quality  of  iron. 
They  last  from  10  to  100  operations,  according  to  the  tempera- 
ture of  the  copper  and  the  care  bestowed  upon  them. 

The  Ansonia  Brass  and  Copper  Company  has  patented  a 
new  mold  for  casting  ingots  directly  from  the  furnace,  without 
the  intervening  process  of  ladling.  While  such  an  improve- 
ment would  relieve  the  workmen  from  the  most  hot  and  labori- 
ous portion  of  the  operation,  the  very  nature  of  the  metal,  its 
high  fusion-point  and  great  heat-conducting  capacity,  cause  it 
to  chill  so  suddenly  as  to  render  the  success  of  such  an  inven- 
tion a  matter  of  some  doubt.  The  same  company  employs  a 
gas  generator  for  heating  a  single  refining-furnace,  and  although 
pronounced  convenient  and  successful,  it  can  hardly  make  any 
great  saving,  considering  the  small  amount  of  fuel  generally 
used  in  ordinary  refining,  and  the  great  expense  of  the  genera- 
tor plant. 

A  great  saving  in  the  expense  of  refining  has  already  been 
made  by  increasing  the  capacity  of  the  ordinary  furnace,  and 
the  next  important  improvement  may  be  looked  for  in  improv- 
ing the  quality  of  the  refined  copper  and  increasing  its  strength 
and  tenacity.  How  this  is  to  be  effected  is  far  too  important 
a  subject  to  be  discussed  within  the  limits  of  a  practical  paper 
on  existing  methods.  Experiments  conducted  by  Mr.  Patch, 
of  the  Detroit  Copper  Company,  as  well  as  the  writer's  per- 
sonal trials,  seem  to  indicate  that  the  presence  of  suboxide  of 
copper  is  by  no  means  essential  to  the  greatest  malleability 
and  strength,  as  believed  by  Percy,  and  that  a  proper  method 


REVEKBERATORY  FURNACES.  325 

of  treatment  may  result  in  the  production  of  copper  having 
a  strength  far  beyond  the  best  brands  at  present  known. 

The  cost  of  refining  varies  so  greatly  with  the  purity  of  the 
blister  copper  treated,  and  depends  also  so  completely  upon  the 
size  of  the  charge,  that  no  absolute  estimate  of  expense  can  be 
given. 

The  following  figures,  taken  from  actual  practice,  give  a  fair 
idea  of  the  cost  of  refining  ordinary  Arizona  pig-copper  of  from 
95  to  98  per  cent. — being  about  equivalent  to  good  Chili  bars. 
The  size  of  the  charge  is  assumed  to  be  sufficient  to  produce 
24,000  pounds  of  refined  metal,  the  furnace  running  regularly, 
and  making  one  charge  every  twenty-four  hours,  while  the  ex- 
pense of  foremen,  etc.,  is  supposed  to  be  divided  between  two 
furnaces. 

Cost  of  refining  one  charge,  yielding  24,000  pounds  of 
copper — 


Coal— best  quality— 3 '8  tons,  at  $5.50 $20  90 

Clay  and  sand  for  fettling— 450  pounds 95 

Cheap  clay  and  loam  for  doors  and  slag-beds — 400  pounds 30 

Poles— 45  feet  of  6-inch  poles,  at  4  cts 1  80 

Charcoal — 6  bushels,  at  10  cts 60 

Proportion  of  cost  of  renewing  bottom 34 

main  arch 62 

"               «           flue  32 

"                "            other  repairs  on  furnace 72 

For  renewing  tools,  barrows,  ladles,  etc 1  11 

Repairs  on  ditto 64 

Lights,  oil,  soap,  clay-wash,  brushes,  etc 70 

Cost  of  resmelting  poorer  slag  in  blister  furnace 1  20 

One  head  refiner 4  00 

One  night  refiner 3  00 

Four  ladles,  at  $2.75 11  00 

Man  fishing  ingots 1  50 

Boy  dumping  molds 75 

Boy  removing  specks  from  ladles  while  pouring 75 

Man  wheeling  copper  to  packing-room 1  50 

One  laborer  about  furnace 1  50 

One  head  packer 2  50 

Two  assistants,  at  $1.50 3  00 

Miscellaneous  expenses  of  packing,  paint,  stencils,  etc 65 

Cost  of  pumping  water  for  boshes 1  15 

Carried  forward  . .  $61  50 


326     MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

Brought  forward $61  50 

Proportion  of  day  and  night  foreman 3  00 

Proportion  of  expense  during  Sundays,  and  other  delays 1  44 

Proportion  of  assaying  necessary  for  control  of  operation 1  12 

Grand  total $67  06 

Cost  per  pound,  *2794  cts. 

This  agrees  closely  with  the  actual  cost  of  running  large 
refining-works  where  prices  closely  approximated  those  as- 
sumed in  this  estimate ;  being  just  three-tenths  of  a  cent,  in- 
cluding general  expenses. 


it 


CHAPTEE  XIII. 

TREATMENT  OF   GOLD   AND  SILVER-BEARING  COPPER  ORES. 

A  VERY  few  words  may  serve  to  indicate  the  present  prac- 
tice in  the  separation  of  the  precious  metals  from  copper. 
The  older  processes  employed  for  this  purpose  were  by  far 
the  most  complicated  and  wasteful  operations  known  to  metal- 
lurgy, and  it  is  only  since  the  discovery  and  introduction  of 
the  various  "  wet "  processes  that  any  but  the  richest  coppers 
could  be  advantageously  treated  for  the  precious  metals. 

The  Ziervogel  process  has  only  been  successful  in  a  few 
isolated  cases,  and  demands  such  pure  material  and  such  skill 
in  manipulation  as  to  debar  its  use  in  ordinary  instances,  nor 
does  it  provide  for  the  extraction  of  gold. 

It  is  indisputable  that  the  electrolytic  methods  are  rapidly 
advancing  to  the  front  in  the  treatment  of  gold  and  silver- 
bearing  metallic  copper,  and  have  the  great  advantages  of  pro- 
ducing a  copper  of  the  best  quality,  but  are  yet  largely  in  the 
experimental  stage,  and  require  a  bulky  and  expensive  plant. 

The  new  Hunt  &  Douglas  method,  as  applied  to  copper 
ores  or  mattes,  seems  to  fill  the  gap  more  completely  than  any 
previous  invention.  By  this  method,  the  copper  is  extracted 
from  the  ore  or  matte  after  a  very  imperfect  roasting,  and 
being  precipitated  as  a  dioxide  by  sulphurous  acid  generated 
from  pyrites,  it  is  decomposed  by  about  one-half  its  weight  of 
metallic  iron,  the  resulting  cement  being  fit  for  immediate  re- 
fining. The  copper  is  obtained  in  a  state  of  absolute  purity 
even  in  the  presence  of  arsenic  and  antimony,  while  the  resi- 
dues, containing  every  trace  of  the  gold,  silver,  and  lead  origi- 
nally present,  may  be  smelted  with  lead  ores  in  a  blast-furnace. 
The  process  has  long  passed  the  experimental  stage,  and  offers 
advantages  peculiar  to  itself  and  unshared  by  any  other. 

The  ease  with  which  the  small  amount  of  gold  sometimes 
present  in  cupriferous  pyrites  may  be  won  is  not  realized  by 


328       MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 


all  copper  smelters,  although  the  method  is  extensively  prac- 
ticed in  this  country,  as  well  as  at  Swansea  and  in  Chili. 

Owing  to  its  great  affinity  for  metallic  copper,  the  gold 
contained  in  white  metal  may  be  concentrated  into  a  very  small 
bulk  of  the  former  by  exposing  the  pigs  of  matte  to  a  slow, 
oxidizing  fusion,  exactly  as  in  the  process  for  making  blister 
copper.  The  operation,  however,  is  interrupted  as  soon  as  a 
certain  quantity  of  metallic  copper  is  formed,  when  the  fur- 
nace is  tapped,  and  the  product — now  advanced  to  pimple 
metal,  or  even  regule,  from  82  to  88  per  cent. — being  examined, 
'bottoms  of  metallic  copper  will  be  found  under  the  first  few 
pigs.  This  is  the  method  pursued  in  making  lest  selected  cop- 
per ;  for  not  only  does  the  small  quantity  of  metallic  copper 
extract  the  gold,  but  also  the  greater  part  of  other  foreign  and 
injurious  substances — such  as  arsenic,  antimony,  tellurium, 
tin,  etc.  The  proportion  of  bottoms  formed  must  vary  with 
the  quantity  of  gold  present ;  in  some  instances,  even  a  repeti- 
tion of  the  processes  being  required  to  fully  extract  the  more 
valuable  metal.  Silver  is  but  slightly  concentrated  by  this 
operation,  as  will  be  observed  from  the  following  assays  made 
under  the  author's  direction,  want  of  space  forbidding  fuller 
details  of  this  important  process : 


Assay  of  original 
white  metal. 

Propor- 
tion of 

Assay  of  bottoms. 

Proportion  thus 
extracted. 

Assay  of  residual 
pimple  metal. 

bottoms 

formed. 

Gold. 

Silver. 

Gold. 

Silver. 

Gold. 

Silver. 

Gold. 

Silver. 

Ounces. 

Ounces. 

Percent. 

Ounces. 

Ounces. 

Percent. 

Per  cent. 

Ounces. 

Ounces. 

0  64 

93-3 

6-4 

9-60 

213-4 

93-7 

14-8 

0-030 

78-7 

2-37 

16-6 

9-0 

19-10 

36-2 

90-2 

18-5 

0-110 

14-2 

o-n 

.... 

5-4 

1-73 

88-4 

.... 

0-012 



In  examining  this  table,  it  must  be  remembered  that  a 
considerable  concentration  has  taken  place  in  the  matte  itself 
as  well  as  in  the  copper  bottoms,  so  that  the  results  do  not 
seem  to  agree  ;  but  the  figures  given  are  sufficient  to  indicate 
the  general  results  of  the  process.  Unless  the  furnace  bottom 
is  already  well  saturated  with  auriferous  metal,  a  heavy  loss 
in  gold  must  be  expected. 


TREATMENT  OF  GOLD   AND  SILVER-BEARING   COPPER  ORES.  329 


_>L  K'n"  _J 

6.0 


SECTION  C.-D. 


In.12    60  123456 

PITTSBUEG  COPPEB  MELTING  PUKNACE.— PIG.   !.   FURNACE  STACK.     PIG.  2.   PtTRNACE  HEARTH. 


CHAPTER  XIY. 

THE   BESSEMERIZING  OF  COPPER  MATTES.* 

WHILE  the  reader  must  be  referred  to  Prof.  Egleston's 
pamphlet,  as  well  as  to  the  literature  of  the  future,  for  all  de- 
tails pertaining  to  this  new  and  interesting  innovation,  the 
present  treatise  would  be  incomplete  without  a  few  remarks 
upon  a  process  which  promises  to  become  of  great  importance 
when  introduced  where  the  conditions  are  suitable  for  its 
application.  So  many  new  and  valuable  improvements  have 
been  greatly  injured  and  retarded  by  their  miscellaneous  and 
improper  application  that  a  few  words  of  advice  from  one  who 
witnessed  the  construction  and  starting  of  the  first  successful 
American  copper  Bessemerizing  plant  may  be  of  value.  While 
there  is  no  doubt  of  the  technical  success  of  the  process  as 
perfected  by  M.  Manhes,  and  constructed  in  this  country 
under  the  direction  of  his  pupils,  it  is  only  under  certain  con- 
ditions that  its  real  usefulness  can  assert  itself,  and  any  at- 
tempt to  apply  it  to  all  and  every  variety  of  circumstances 
would  certainly  result  disastrously. 

The  Bessemerizing  plant,  as  constructed  at  the  works  of 
the  Parrot  Silver  and  Copper  Company  at  Butte  City,  and 
observed  by  the  writer  at  its  commencement,  was  adapted  to 
two  different  duties  :  1st.  To  receiving  copper  matte  of  a  low 
grade — from  15  to  40  per  cent. — and  bringing  it  up  to  white 
metal — 75  per  cent. ;  or,  2d.  To  bringing  white  metal  up  to  a 
very  pure  blister  copper. 

The  impossibility  of  producing  metallic  copper  from  poor 
matte  at  one  continuous  operation  is  quite  evident,  as,  aside 
from  the  difficulty  of  dealing  with  the  great  quantity  of  slag 
formed  from  the  iron  and  other  foreign  bases  contained  in  the 
low-grade  matte,  the  amount  of  metallic  copper  produced 

*  See  School  of  Mines  Quarterly  for  May,  1885,  for  paper  on  this  subject, 
by  T.  Egleston. 


THE   BESSEMERIZING  OF  COPPER  MATTES. 


331 


Fig.3 


SECTION  E.-F. 


FRONT  ELEVATION 

PITTSBUKG  COPPER   MELTING-FURNACE.— FIGS.  3  AND  4.       ROOF  COVER    ARCH  AND  FURNACE 

STACK. 

I 


332      MODERN  AMERICAN  METHODS   OF  COPPER  SMELTING. 

therefrom  would  be  too  small  for  manipulation.  For  instance, 
the  usual  charge — 2,000  pounds  of  a  20  per  cent,  matte — 
would  yield  less  than  400  pounds  of  blister  copper,  a  quantity 
far  too  small  to  submit  to  any  blowing  operation  in  a  converter. 

This  is  especially  the  case  in  M.  Manhes's  converter,  where 
the  tuyere  orifices  are  situated  at  some  distance  above  the 
bottom  of  the  vessel.  This  latter  peculiarity  has  been  found 
an  essential  element  of  success ;  for,  whereas  in  iron,  the 
whole  contents  of  the  converter  are  homogeneous,  the  blast 
traversing  the  entire  mass  of  metal,  and  oxidizing  the  impuri- 
ties, which  may  be  regarded  as  distributed  equally  throughout 
the  molten  iron,  so  that  the  whole  product  gradually  becomes 
pure  without  any  division  into  a  finished  and  still  uncom- 
pleted portion — in  treating  copper  matte  above  75  or  80  per 
cent.,  the  liquid  metal  that  until  that  point  has  been  homo- 
geneous throughout,  must  then  begin  to  separate  into  two  por- 
tions— namely,  sulphide  of  copper,  and  metallic  copper  that 
has  been  deprived  of  its  sulphur  by  oxidation.  As  the  process 
continues,  the  latter  product  augments  in  quantity,  while  the 
former  decreases,  until  the  last  atom  of  sulphur  is  removed. 
Were  the  tuyeres  at  the  bottom  of  the  converter,  the  metallic 
copper  would  soon  chill  and  obstruct  them,  and  it  was  not 
until  M.  Manhes  raised  them  to  such  a  height  as  to  allow  the 
quiet  subsidence  of  the  metallic  product  below  their  inlets, 
that  he  attained  complete  success.  It  is  necessary,  however, 
that  a  sufficient  amount  of  copper  be  present  to  support  the 
superincumbent  layer  of  liquid  matte  above  the  tuyere  open- 
ings, so  that  the  blast  may  traverse  a  molten  and  oxidizable 
product  to  the  last,  and  thus  generate  sufficient  heat  to  main- 
tain the  entire  mass  in  a  liquid  condition. 

Experience  has  shown  that  upon  introducing  a  matte  con- 
taining from  72  to  75  per  cent,  of  copper  into  the  converter, 
the  process  advances  with  great  rapidity  and  completeness, 
while  a  matte  of  60  or  65  per  cent,  requires  several  times  as 
long  for  its  oxidation.  On  the  other  hand,  a  low-grade  matte 
of  even  15  or  20  per  cent,  advances  with  satisfactory  speed  to 
the  condition  of  white  metal — from  70  to  75  per  cent. — and 
there  stops  or  continues  very  slowly.  The  practice  has,  there- 
fore, been  adopted  of  interrupting  the  oxidation  of  the  low- 


THE   BESSEMERIZING  OF   COPPER  MATTES. 


333 


Fig.5 


£_£. 


28' 


PITTSBUKG  COPPER  MELTING  FURNACE— FIG.   5.   INGOT  MOLD. 


334    MODERN  AMERICAN  METHODS   OF   COPPER  SMELTING. 

grade  matte  at  the  point  indicated,  pouring  out  of  the  conver- 
ter, that  it  may  separate  from  the  slag,  and  subsequently 
completing  the  process  in  a  second  vessel,  the  products  of  two 
or  more  "blowings"  of  poor  matte  being  united  to  form  a 
single  charge  for  blister  copper. 

It  is,  therefore,  necessary  for  economy  to  have  two  sets  of 
converters,  and  while  three  converters  are  required  for  a  sin- 
gle operation,  five,  or  possibly  four,  converters  are  sufficient 
for  the  complete  process.  A  converter  will  usually  stand  from 
eighteen  to  twenty-four  blows  (twenty-four  hours)  without  re- 
pairs, so  that  for  the  single  operation,  one  converter  is  under- 
going repairs,  the  second  is  drying,  while  the  third  is  in  use. 

In  France,  a  separate  cupola  is  used  for  melting  the  matte 
for  the  converter ;  but  the  Parrot  Company  has  found  it 
feasible  to  run  the  matte  directly  from  the  ore  blast-furnace 
to  the  converter. 

No  fuel  is  required  to  keep  up  the  temperature  in  the  con- 
verter while  working  on  low-grade  matte  ;  but  the  operation 
for  blister  copper  requires  the  occasional  use  of  a  few  pounds 
of  coke  to  keep  up  the  necessary  high  temperature. 

While  the  construction  of  the  converter  plant  is  simple,  the 
management  of  the  same  requires  much  care  and  experience.* 

The  appearance  of  the  flame  issuing  from  the  mouth  of  the 
vessel  is  of  little  value  as  a  guide,  owing  to  its  changeable  color 
from  the  various  foreign  constituents  of  the  matte.  The  tuy- 
eres require  constant  opening  with  an  iron  rod,  taking  one 
man's  whole  time. 

The  lining  of  the  boiler-iron  converter  is  of  crushed  quartz 
(or  pure  siliceous  sand),  mixed  with  enough  plastic  fire-clay  to 
hold  it  together.  It  is  rammed  in  large  balls,  the  original 
shape  and  size  of  the  interior  vessel  being  obtained  from  an 
oil  barrel,  used  as  a  core,  about  which  the  lining  is  rammed. 
The  same  material  is  used  for  repairs.  A  cylinder  blowing- 
engine  supplies  the  blast,  which  is  much  less  powerful  than  in 
ordinary  Bessemer  work,  the  height  of  the  liquid  column  of 
metal  being  only  a  few  inches,  and  the  entire  charge  not  ex- 
ceeding 2,200  pounds. 

Any  attempt  at  estimating  the  saving  effected  by  this  opera- 

*  The  Parrot  Company's  plant  was  erected  by  pupils  of  M.  Manhes. 


THE   BESSEMERIZING  OF  COPPER  MATTES.  335 

tion  under  any  given  circumstances  would  be  futile,  as  the  pro- 
cess, although  satisfactory  to  its  owners,  and  thoroughly  suc- 
cessful in  the  opinion  of  the  author — speaking  as  a  spectator 
— is  still  under  constant  improvement,  and  when  stripped  of 
its  crudities  and  adapted  to  American  conditions,  will  give 
very  different  results  from  those  obtained  at  its  first  introduc- 
tion. 

There  is  every  reason  to  believe  that  its  capacity  will  be 
greatly  increased,  and,  as  even  in  its  present  state  it  can  show 
a  great  saving  in  fuel  and  labor  above  any  of  the  older 
methods,  there  is  little  doubt  that  it  will,  ere  long,  be  recog- 
nized as  an  essential  feature  of  every  large  copper  plant, 
except  where  very  cheap  fuel  or  other  peculiar  conditions 
neutralize  its  advantages.  The  elimination  of  arsenic  and 
antimony  by  this  operation  was  highly  satisfactory,  as  far  as 
the  author's  observations  extended. 

"Whether  an  undue  loss  of  silver  by  volatilization  may  also 
occur  in  argentiferous  mattes,  yet  remains  to  be  decided.  The 
slags  from  the  Bessemerizing  of  low-grade  mattes  form  a  wel- 
come basic  flux  in  the  ore-furnace,  while  the  lining  of  the  con- 
verter is  partially  protected  from  their  corrosive  influence  by 
the  feeding  of  pulverized  siliceous  ores  through  the  tuyere- 
holes  with  the  blast. 

Latest  advices  from  the  President  of  the  Parrot  Company 
report  great  improvements  in  the  capacity  and  economy  of  the 
process. 

A  simple  set  of  converters  now  produces  50,000  pounds 
of  99  per  cent,  copper,  daily  from  60  per  cent,  matte,  and 
casts  of  2,400  pounds  of  pig-copper  are  now  made  from  a 
single  charge  of  matte  of  this  grade. 


(THE  END.) 


INDEX. 


Agglomeration  of  fine  Ore  in  Calcin- 
ing Furnaces,  267. 

Ames,  F.,  168. 

Ammonia,  Effect  of,  on  the   Cyanide 
Assay,  24. 

Anaconda  Copper  Ores,  6. 

Analysis  of  a  Furnace  Chill,  190. 

Analysis  of  Calcined  Ore,  164. 

Analysis  of  Melaconite,  12. 

Analysis  of  Pig  Copper,  264. 

Analysis  of  Rio  Tinto  Pyrites,  110. 

Analysis  of  Roasted  Ores,  168. 

Analysis  of  Santa  Rita  Concentrates, 
11. 

Analysis  of  Slag  at  the  Copper  Queen 
Furnace,  204. 

Analysis  of    Slag,    Detroit   Smelting 
Works,  Arizona,  205. 

Areas  of  Smelting  Furnaces,  210. 

Arsenic  and  Antimony,  effects  of,  on 
the  Cyanide  Assay,  22,  24. 

Assaying,  Cost  of  Sampling  and,  30. 

Assaying,  Methods  of  Copper,  16. 

Assay  Methods,  20. 

Assays  of  Ore  before  and  after  Roast- 
ing, 70,  74. 

Assays   of   Parrot   Company's    Matte 
and  Slag,  301. 

Assay  Percentage  of  Copper  in  Slag, 
247. 

Atlantic  Coast  Beds,  1. 

Atvidaberg    Black    Copper,  Analysis 
of,  265. 

Automatic    Revolving    Hearth    Fur- 
naces, 130. 

Azurite  at  Longfellow  Mine,  Arizona, 
13. 

Azurite,  distribution  of,  13. 

Baker  Blowers,  256. 

Baker  Blowers  for  Smelting  Furnaces, 
209. 

Ball  Pulverizer,  120. 

Battery  Assay,  accuracy  of  the,  29. 

Battery   Assaying,    effect   of  various 
substances  on,  25. 

Battery  Assaying,  Materials  used  in, 
26. 

Bedded  Copper  Veins,  3. 

Bessemerizing  Copper  Mattes,  330. 
22 


Bessemerizing  Plant  at  the  Parrot 
Company's  Works,  330. 

Silver  and  Bismuth,  effect  on  the 
Cyanide  Assay,  23. 

Black  Copper  from  Mansfeld,  Prussia, 
analysis  of,  265. 

Black  Oxide  of  Copper,  occurrence 
of,  2. 

Blast  Furnace  Accessory  Apparatus, 
259. 

Blast  Furnace  Smelting,  General  Re- 
marks on,  173,  246. 

Blast  Furnace  Smelting  in  Vermont, 
174. 

Blat4  Furnaces  of  Brick,  215. 

Blast  Furnaces,  treatment  of  fine  Ore 
in,  266. 

Blast  Pipe  for  Orford  Furnace,  252. 

Blast  Pressure  in  Smelting  Furnaces, 
210. 

Blister  Copper,  Making  of,  306. 

Blister  Copper  Smelting,  Composition 
of  Slag  and  Copper  from,  310. 

Blister  Copper,  Tapping  of,  309. 

Blowers  and  Blast  Apparatus,  255. 

Blotving-in  the  Furnace,  202. 

Bogardus  Mill,  the,  183. 

Bornite  or  Erubescite,  Distribution  of, 
14. 

Bornite,  Percentage  of  Copper  in,  15. 

Brick  Blast  Furnaces,  175  215. 

Brick  Furnaces  for  Copper  Smelting, 
249. 

Brick  Furnaces,  the  Cost  of,  241. 

Bricking  Fine  Ore,  267. 

Bricking  Pyrites  Fines  in  England, 
271. 

Bruckner's  Roasting  Cylinder,  128. 

Brunton  Ca'ciner,  134. 

Brunton's,  D.  W.,  Automatic  Sam- 
pling Machine,  17. 

Butte  District,  Montana,  Copper  Pro- 
duction of,  7. 

Butte,  Montana,  Copper  Ores,  Aver- 
age Value  of,  7. 

Butte,  Montana,  Mines.  14. 

Calcination  of  Ore  and  Matte  Fines, 
115. 

Calcined  Ore,  Analysis  of,  164. 


338 


INDEX. 


Calcining  Fu ran ces,  126. 

Calcination  of  Copper  Ores,  37. 

Calcining  Process,  the  Chemistry  of 
the,  157. 

Calumet  and  Hecla  Mines,  Michi- 
gan, 4. 

Calumet  and  Hecla  Mineral,  Assay 
of,  35,  36. 

Capelton  Mines,  Canada,  3. 

Carbonate  Deposits  of  the  Southwest, 
8. 

Carbonate  Deposits  of  Clifton, A.  T.,  9. 

Car,  Ore  Dumping,  56. 

Centrifugal  Fan  Blowers,  255,  257. 

Chimneys,  Construction  of,  147. 

Chimneys  for  Calciners,  Dimensions 
of,  150. 

Chimney,  Height  of,  for  Open  Stalls, 
90. 

Chimneys,  Sizes  of,  for  different  Fur- 
naces, 1(J8. 

Church,  Prof.  J.  A.,  Experiments  on 
Bricking  Ore  at  Tombstone,  Ariz., 
271. 

Chalcocite,  Copper,  Percentage  of,  14. 

Chalcopyrite,  Distribution  of,  13,  14. 

Chal  copy  rite,  Occurrence  of,  2. 

Charges  for  Copper  Furnaces,  251. 

Charges  for  Copper  Furnaces,  Relative 
Advantages  of  Large  and  Small, 
249. 

Charging  a  Blast  Furnace,  226. 

Chemistry  of  the  Calcining  Process, 
157. 

Chili  Copper  Ores,  7. 

Chili  Mills,  121. 

Chilling  a  Furnace,  189. 

Chills  in  Blast  Furnaces,  method  of 
Removing,  236. 

Colorimetric  Determination  of  Cop- 
per, 25. 

Composition  of  Slag  and  Copper  from 
Blister  Copper  Smelting,  310. 

Concentrating  Effect  of  Roasting,  70. 

Concentration  of  Copper  Bottoms,  328. 

Concentration  of  Copper  in  Roasting, 
76. 

Concentration  of  Matte  by  Oxidizing 
Fusion,  306. 

Consumption  of  Aathracite  in  Smelt- 
ing, 209. 

Cooper  and  Patch  on  Reverberatory 
Furnace  Stacks;  153. 

Cooper  Assaying,  Methods  of,  16. 

Copper  in  Slag,  Percentages  of,  251. 

Copper  Glance  in  Montana  Mines,  14. 

Copper  Melting  Furnace  used  at  Pitts- 
burgh, 329. 

Copper,  Native  Metallic,  11. 

Copper  Ores,  Treatment  of  GoM  and 
Silver  Bearing,  327. 


Copper  Pigs,  Weight  of,  260. 

Copper  Precipitation  with  Zinc,  24. 

Copper  Queen  Furnaces,  199. 

Copper  Queen  Mine,  Arizona,  9. 

Copper  Queen  Smelter,  Work  done 
by,  200. 

Copper  Refining,  310. 

Copper  Refining  Furnaces,  311. 

Cornish  Rolls,  121. 

Cost  per  Ton  for  Breaking  and  Sizing 
Ores,  42,  43. 

Cost  of  Building  and  Running  Brick 
Furnaces,  241. 

Cost  of  Building  Reverberatory  Fur- 
naces, 292. 

Cost  of  Calcining,  169. 

Cost  of  Calcining  Furnaces,  155. 

Cost  of  Cupola  Smelting,  243. 

Cost  of  Grate  Bars,  106. 

Cost  of  Materials  for  Mason  Work, 
102. 

Cost  of  Matte  Roasting,  81. 

Cost  of  Railroad  Tracks,  103. 

Cost  of  Refining  Copper,  325. 

Cost  of  Reverberatory  Furnace  Bot- 
toms, 297. 

Cost  of  Roasting  in  Heaps,  74. 

Cost  of  Running  the  Reverberatory 
Furnace,  297. 

Cost  of  Smelting  in  Brick  Furnaces, 
245, 

Cost  of  Smelting  in  the  Herreshoff 
Furnace,  194. 

Crushing  Machinery,  118. 

Cuprite,  Occurrence  of,  at  Santa 
Rita,  5,  11. 

Cuprite,  or  Red  Oxide  of  Copper,  Dis- 
tribution of,  11. 

Cyanide  Assay,  Effect  of  Different 
Substances  on  the,  20,  23. 

Decrepitation  during  Calcination,  116. 

Description  of  Railroads  for  Heap 
Roasting,  56. 

Douglas's  Roasting  Cylinder,  128. 

Dry  Sweating,  Vivian's  Method  of, 
322. 

Dumping  Car  for  Ore,  56. 

Effect  of  Excess  of  Silica  in  Blast 
Furnace,  226. 

Egleston,  Prof.  T.,  207. 

E^leston  on  Refining  Copper,  311. 

Egleston's  Monograph  on  Copper  Re- 
fining, 282. 

Electrolytic  Assay,  Effect  of  Various 
Sub-tances  on,  25. 

Electrolytic  or  Battery  Assaying,  25. 

Ely  Mines,  Vermont,  3. 

Ely  Pig  Copper,  Analysis  of,  264. 

Engineering  and  Mining  Journal,  23, 
60. 

Eustis,  W.  E.  C.,  216. 


INDEX. 


339 


Eustis',  W.  E.  C.  Experiments  on 
Bricking  Hne  Ores,  269. 

Fettling  Reverberatorv  Furnaces,  290. 

F.ne  Ore  in  Blast  Furnaces,  Treat- 
ment of,  206. 

Fine  Ore,  Methods  for  Bricking,  267. 

Fines,  in  reducing  Quantity  Smelted, 
Effect  of,  273. 

Fines,  Percentage  Allowable  in  Heap- 
Roasting,  41. 

Fines,  Percentage  Produced  by  Differ- 
ent Crushing  Machines,  40. 

Fines  Used  in  Charge,  Proportion  of, 
273. 

FTC  Assay  of  Lake  Superior,  31. 

Fire  Brick,  Comparative  Values  of, 
253 

Firing  Open  Stalls,  92. 

Firing  up  Reverberatory  Furnaces, 
287. 

Fluxing  Materials  Compared,  262. 

Fluxes  Used  in  Lake  Superior  Fire 
Assay,  34. 

Fore-Hearth,  External,  209. 

Fore-Hearth,  of  the  Copper  Queen 
Furnaces,  210. 

Fuel,  on  Quality  of  Copper  Produced, 
Effect  of,  265. 

Fuel  for  Copper  Refining  Furnaces, 
312. 

Fuels  in  the  Blast  Furnace,  Compara- 
tive Values  of,  253. 

Fuel  Used  in  Reverberatory  Furnaces, 
Quantity  of  291. 

Fumes,  Effect  of,  on  Vegetation  50. 

Furnace,  Amount  Smelted  in  Differ- 
ent Sized  Furnaces,  194. 

Furnace,  Brueckner's,  128. 

Furnace, Charging  a  BlastFurnace,226. 

Furnace,  Construction  of  Reverberu- 
tory  Refining  Furnace,  311. 

Furnace-Campaign,  Duration  of  a, 
204. 

Furnace,  for  Lake  Superior  Fire  As- 
say, 32,  34. 

Furnace,  Gerstenhofer  Shelf,  127. 

Furnace,  James  Douglass',  128. 

Furna:e,  Lake  Superior  Refining  Fur- 
nace, 313. 

Furnace,  Method  of  Blowing-in,  202. 

Furnace,  Repairing  a  Blast  Furnace, 
238. 

Furnace, Reverberatory  Calcining,  134. 

Furnace,  Revolving  Cylinder,  128. 

Furnace  Stacks,  Construction  of,  147. 

Furnace  Sta.cks,  Cooper  &  Patch's  Re- 
marks on,  153. 

Furnace,  the  Brunton,  134. 

Furnace,  the  Howell,  127. 

Furnace,  the  Lake  Superior  Smelting, 
207. 


Furnace,  the  O'Hara  Mechanical,  130. 

Furnace,  the  Orford  Brick,  216. 

Furnace,  the  Parke,  134. 

Furnace,  the  Reverberatory,  278. 

Furnace,  the  Spence  Automatic,  130. 

Furnace,  the  Stetefeldt,  127. 

Furnace,  Water  Jacket,  175. 

Furnaces,  Charging  Reverberatory, 
289. 

Furnaces,  Construction  of  Reverbera- 
tory, 279. 

Furnaces,  Cost  of  Calcining,  155. 

Furnaces,  Cost  of  Smelting  in  Brick, 
245. 

Furnaces  for  Copper  Refining,  311. 

Furnaces  for  Roasting  and  Calcining, 
126. 

Furnaces,  Management  of  Reverbera- 
tory, 289. 

Galena  Roasting,  160. 

Gap  Nickel  Mine  in  Pa.,  Bricking 
Fines  at  the,  268. 

Gaylord,  J.  E.,  86. 

German  Copper  Smelting,  172. 

Gerstenhofer  Shelf  Furnace,  127. 

Gilpin  Co.,  Colorado,  Copper  Veins 
of,  7. 

Glenn,  Mr.  William,  60. 

Gold  and  Silver  Bearing  Copper  Ores, 
Treatment  of,  327. 

Grand  Belt  Copper  Deposits,  Tex.,  10. 

Grant  Smelting  Works'  Improvement 
in  Tapping,  261. 

Grate  Bars,  Cost  of.  106. 

Green  Fines  in  the  Blast  Furnace, 
Smelting,  274,275. 

Heap  Matte,  Assay  of,  70. 

Heap  Roasting,  48. 

Heap  Roasting,  Cost  of,  74. 

Heap  Roasting,  Description  of,  59. 

Heap  Roasting,  Illust-ations  of,  55. 

Heap  Roasting  in  Vermont,  60. 

Heap  Roasting,  Management  of,  65. 

Heap  Roasting  of  Matte,  77. 

Heap  Roasting,  Reasons  for  and 
against  its  adoption,  50. 

Heap  Roasting,  Results  of,  at  Ely, Ver- 
mont, 74. 

Heap  Roasting,  Time  consumed  in, 
58. 

Hearth  Sand,  Analysis  of,  285. 

Henrich,  M.  L.  Carl,  205. 

Herreshoffs  first  Water  Jacket,  190. 

Herreshoff's  Furnace,  Ib5. 

Hot  Blast  for  Copper  Smelting,  248. 

Howell  Roasting  Furnace,  127. 

Howe,  H.  M.,  216. 

Howe,  H.  M.,  on  Copper  Smelting, 
277. 

Howe's  Experiments  on  Blowers,  258. 

Hunt  &  Douglas  Process,  327. 


340 


INDEX. 


Ingot  Molds  for  Copper,  324,  3?6. 

James,  Mr.  S.,  205. 

Jaw  Crushers,  119. 

Kernel  Roasting  at  Agordo,  Italy,  75. 

Kiln  Roasting  of  Matte  at  Mansfeld, 
Germany,  113. 

Lake  Superior  Pig  Copper,  Analysis 
of,  265. 

Lake  Superior  Copper  Deposits,  4. 

Lake  Superior,  Fire  Assay,  31. 

Lake  Superior  Fire  Assay,  Accuracy 
of,  35. 

Lake  Superior  Smelting  Furnaces, 
209. 

Leaching  Copper  Ores  in  California, 
10. 

Lead,  Effect  of,  in  Copper  Assays,  24. 

Lime,  Effect  of,  on  the  Cyanide  As- 
say, 24. 

Liine  in  Bricking  Fine  Ore,  Use  of, 
268. 

Lines  of  a  Furnace  before  and  after  a 
Campaign,  231. 

Losses  of  Copper  in  Roasting,  168. 

Loss  of  Copper  in  Smelting,  300. 

Loss  of  Copper  in  Smelting  at  the  Par- 
rot Works,  301. 

Lunge's  work  on  Sulphuric  Acid.  109. 

Magnesia,  Effect  of,  on  the  Cyanide 
Assay,  24. 

Manhes'  Bessemerizing  Process,  330. 

Manhes'  Converter,  332. 

Mansfeld,  Germany,  Copper  Deposits, 
10. 

Mansfeld  Kiln  Roasting  of  Matte, 
113. 

Matte  Concentration  by  Oxidizing  Fu- 
sion, 306. 

Matte,  Heap  Roasting  of,  77. 

Matte,  Percentage  of  Copper,  in  Heap, 
70. 

Matte,  Percentage  of  Copper  in  Swan- 
sea, 300. 

Matte  Roasting  at  the  Copper  Queen, 
211. 

Matte  Roasting  in  Heaps,  Cost  of,  81. 

Matte  Roasting  Stalls,  Dimensions  of, 
107. 

Mattes,  Bessemerizing  of  Copper,  330. 

Matte-Smelting  in  Blast  Furnaces, 
261,  263. 

Matte  Stalls,  Management  of.  106. 

Matte-Tapping,  Methods  of,  260. 

Mechanical  Preparation  of  Ore  for 
Roasting,  39. 

Melting  Furnace,  Pittsburgh  Copper, 
329. 

Melaconite,  or  Black  Oxide  of  Copper, 
Distribution  of,  12. 

McKenzie  Blowers,  256. 

Molds  for  Casting  Ingots,  324. 


Montana  Copper  Deposits,  6. 

Moose  Mine,  Colorado,  Experiments 
on  Smelting  Fines,  272. 

Mountain  System  of  Veins,  5. 

Mount  Lincoln,  Col.,  Experiments  in 
Roasting,  161. 

Murphy,  Mr.  D.  P.,  Chemist,  300. 

Multiple  Jaw  Crushers,  Blake's,  121. 

Nacimiento  Copper  Deposits,  New 
Mexico,  10. 

Native  Metallic  Copper,  11. 

Nevada  County,  California,  Copper 
Veins,  10. 

Newfoundland  Copper  Deposits,  3. 

O'Hara's  Mechanical  Furnace,  130. 

Open  Stall  Roasting,  82. 

Orange  Mountain,  New  Jersey,  Cop- 
per Ores  of,  14. 

Ore  and  fuel,  Proportions  in  Copper 
Furnaces,  250. 

Ore  Breaking  and  Sizing,  Cost  of,  43. 

Ore  Knob,  North  Carolina,  Copper  De- 
posits, 3. 

Ore  Knob  Pig  Copper,  Analysis  of,  265. 

Ore  Hoastiug  in  Lump  form  in  Kilns, 
109. 

Ore  Smelting  for  Coarse  Metal,  299. 

Ores  of  Copper,  Description  of,  11. 

Ores  of  Copper.  Distribution  of,  1. 

Orford  Brick  Furnace,  216. 

0 1 ford  Company's  Method  of  Brick- 
ing Fines,  269. 

Orfoid  Company's  Slag  Pots,  254. 

Orford  Copper  Furnace,  Blast  Pipe 
arrangement  of,  252. 

Orford  Furnace,  Results  of  Smelting 
Green  Fines  in  the,  275. 

Orford  Nickel  &  Copper  Co.,  Kiln 
Roasting,  112. 

Oscura  Copper  Deposits,  New  Mexico, 
10. 

Oxygen  in  Copper,  323. 

Parke  Furnace,  134. 

Parrot  Company's  Bessemerizing 
Plant,  330. 

Parrot  Copper  Company's  Open  Stalls, 
88. 

Parrot  Copper  Company,  Work  of  the 
Furnaces  of  the,  300. 

Parrot  Copper  Vein,  6. 

Parrot  Works,  Experiments  on  Brick- 
ing Ores  at  the,  270. 

Patch  &  Cooper  on  Furnace  Stacks, 
153. 

Patch,  Maurice  B.,  on  Lake  Superior 
Assay,  31. 

Pig  Copper,  Analysis  of,  264. 

Plattner's  Work  on  Host  Processe,  38. 

Power  required  for  Blowers,  258. 

Pressure  of  Blast  in  Copper  Smelting, 
247,  248. 


INDEX. 


341 


Pressure  of  Bla^t  in  Smelting  Fur- 
naces, 210. 

Production  in  Smelting,  247. 
Proportions   of  Ores   at    the   Copper 

Queen,  211. 
Proportion  of  Ore  to  Charge  in  Blast 

Furnace,  210. 
Proportions  of  Ore  to  Fuel  in  Blast 

Furnaces,  210. 
Pyrite  and  Pyrrhotite,  2. 
Pyrites  from  Canada,  Analysis  of,  111. 
Pyrites  from  Rio  Tinto,  Analysis  of, 

110. 

Pyrites  from  Virginia,  111. 
Pique  Mine,  the  Deepest  in  Chili,  7. 
Quantity  Smelted  in   Blast  Furnaces 

per  24  hours,  210. 
Kailroad  Tracks,  Cost  of,  103. 
Raschette,    Furnace    of    the    Orford 

Copper  and  Sulphur  Co  ,  216,  218. 
Refining  Copper,  310. 
Refining  Copper,  Cost  of,  325. 
Refining  Furnaces,  Charging  of,  318. 
Refining  Furnaces, Production  of,  312. 
Regule,  Percentage  of  Copper  in,  328. 
Relative  Proportions  of  Ore  to  Fuel  in 

Copper  Furnaces,  250. 
Repairs  of  Blast  Furnaces,  239. 
Reverberatory  Calciuer,  Construction 

of,  138. 

Reverberatory  Calciners,  134. 
Reverberatory     Calcining      Furnace, 

Length  of,  137. 

Reverberatory   Furnace   at  Lake   Su- 
perior Smelting  Works,  313. 
Reverberatory  Furnaces,  278. 
Reverberatory  Furnaces,  Construction 

of,  279. 

Reverberatory  Furnaces, Cost  of  Build- 
ing, 292. 
Reverberatory   Furnaces,   Firing  up, 

287. 
Reverberatory  Furnaces,  Proportions 

of,  282. 
Reverberatory  Furnaces,  Quantity  of 

Materials  used  in  Building,  292. 
Reverberatory       Furnace,      Quantity 

Smelted  in  per  day,  299. 
Reverberatory  Furnaces,  Size  of  Fire 

Box,  291. 
Reverberatory     Furnaces,     Size     of 

Hearth,  291. 
Reverberatory  Furnaces,  Work  done 

by,  291. 

Revolving  Cylinder  Roasters,  128. 
Richards,  Prof.  R.  H.,  196. 
Rio  Tinto  Ore,  Analysis  of,  110. 
Roasted  Ore,Percenfageof  inHeaps,71. 
Roast  Heaps,  Effect  of  Rain  on,  67. 
Roasting  Fines  at  the  Parrot  Mines, 

Montana,  116. 


Roasting  in  Heaps,  48. 
Roasting  in  Open  Stalls,  82. 
Roasting  Lump  Ores  in  Kilns,  109. 
Roasting,  Mechanical    Preparation  of 

Ore  for,  39. 

Rousting  of  Copper  Ores,  37. 
Roasting  of  Copper  Ores,  ai.d  Furnace 

Products,  89. 

Mineral  Resources  of  the  U.  S.,  39. 
Roasting  Ore  and  Matte  Fines,  115. 
Roasting,  Percentage  of  Different 

Sizes  of  Ores  u-ed  in,  41. 
Roasting  Stalls,  Cost  of,  100. 
Roast  Piles,  Laying  Out  the  Ground 

for,  52. 

Roast  Piles,  Sizes  of,  53. 
Rolls  of  Chilled  Iron,  123. 
Rolls  for  Ore  Crushing,  121. 
Root  Blowers,  256. 
Russian  Copper  Deposits,  10. 
Slag,  from    Furnace,  Transportation 

of,  253. 
Smelting,  Cost  of  in   the  Herreshoff 

Furnace,  194. 

Smelting  for  White  Metal,  304. 
Smelting,  General  Remarks  on  Blast 

Furnace,  246. 
Smelting  in  Reverberatory  Furnaces, 

279. 

Smelting  of  Copper,  170. 
Smelting  of  Sulphides  in  the  Blast 

Furnace,  173. 

Smelting,  the  Cost  of  Cupola,  243. 
Smelting,    Use    of    Heated    Blast  in 

Copper,  248. 

Southern  Carbonate  Deposits,  8. 
Spall  ing,  Cost  of,  45  &  48. 
Spence    Automatic    De-sulphurizing 

Furnace,  130. 
Stall  Roasting,  82. 

Stall    Roasting,  Advantages  and  Dis- 
advantages of,  95. 
Stall  Roasting,  Cost  of,  98. 
Stall  Roast  ng,  Firing  open  Stalls,  92. 
Stall  Roasting  in  Tennessee,  98. 
Stall  Roasting,  Losses  of  Copper  in, 

97. 

Stall  Roasting  of  Matte,  105. 
Stall  Roasting,  Sizes  of  Stalls,  89. 
Stall  Roasting,  Time  Necessary  for, 

94. 

Stalls  for  Matte,  Management  of,  106. 
Stalls  for  Roasting  Matte,  Dimensions 

of,  107. 

Sampling  Lake  Superior  Mineral,  32. 
Sampling  Machine,  Brunton's,  17. 
Sampling  of  Ores,  16. 
Santa  Rita,  New  Mexico,  Copper  De- 
posits, 4. 
San   Juan   Region,  Colorado,  Copper 

Deposit?,  8. 


342 


INDEX. 


Screens  for  Sizing  Ores,  41,  42. 

Shaft  Furnace  for  Roasting,  126. 

Shells  of  Steel  for  Rolls,  123. 

Siphon  Tap,  260. 

Siphon  Tap  in  Smelting  Green  Fines, 
use  of,  275. 

Slag  Analysis  of  Copper  Queen,  204. 

Slag-,  Analysis  of  Detroit  Smelting 
Works,  Arizona,  205. 

Slag  Brick,  the  Manufacture  of,  83. 

Slag  Cupola,  at  Lake  Superior,  207. 

Slag  Dumps,  255. 

Slag  from  Matte  Smelting,  uses  of, 
262. 

Slag  Pots,  254. 

Slag  Pots  Necessary,  the  Number  of, 
254. 

Slag  Tapping,  intervals  between,  260. 

Stalls,  Labor  in  Building,  103. 

Stamps  for  Crushing,  120. 

Steep,  Manufacture  of,  183. 

Stetefeldt  Furnace,  127. 

Stone  Hill,  Alabama,  Copper  Depos- 
its, 3. 

Stoppages  in  Cupola  Smelting,  232. 

Sturtevant  Blowers,  257. 

Sturtevant  Mill,  The,  184. 

Sulphur,  Collecting  from  Roast  Heaps, 
66. 

Sulphurous  Acid  Gas,  Effect  on 
Vegetation,  50. 

Sump-Ofen,  the  German,  180. 

Swansea  Copper  Smelting,  171. 

Swansea,  Smelting  for  Coarse  Metal, 
299. 

Talbot,  J.  F.,  168. 

Tallapoosa  Mine,  Georgia,  3. 

Tamarack  Mine,  Michigan,  4. 

Tapping,  Effect  on  the  Grade  of  Matte- 
in,  Reverberatory  Process,  308. 

Tetrahedrite  or  Gray  Copper  Ore,  Dis- 
tribution of,  15. 

Thomson,  J.  L.,  216,  232. 


Thomson,    J.    L.,    Experiments     on 

Smelting  Green  Fines,  274. 
Thomp^on,  R.  M.,  216. 
Tiegel-Ofen,  the  German,  180. 
Time  Consumed  in   Heap   Roasting, 

58. 

Time  Required  for  Calcination,  167. 
Titration  with  Potassium  Cyanide,  20. 
Tools  for  Roasting  Furnaces,  147. 
Tools    Required     for     Reverberatory 

Furnaces,  296. 

Torrance,  Prof.  J.  Fraser,  269. 
Torrey  and  Eaton,  on  the  Accuracy  of 

the'Cyanide  Assay,  21. 
Tuyeres,  Area  of,  240. 
Tuyeres,    Number    of,    in    Smelting 

Furnaces,  240. 

Utilizing  Laboratory  Wastes,  30. 
Virginia  Copper  Deposits,  3. 
Vivian,  Henry  Hussey,  179. 
Vivian  Method  of  Dry  Sweating,  322. 
Walker  River  Mines,  Nevada,  10. 
Water,  Amount  Necessary  for  Water 

Jacket  Furnaces,  177,  201. 
Water     Jacket     Cupola    for    Copper 

Smelting,  248,  176. 
Water  Jacket  Furnaces,  175,  260. 
Water  Jacket  Furnaces,  Capacity  and 

Duration  of,  213,  214. 
Water  Jacket  Furnaces,  Construction 

and  Management  of,  195,  201. 
Well,  First  Furnace  Well  Built  in  this 

Country,  179. 
Wendt  A.  F.,  on  Losses  in  Roasting, 

97. 
White  Metal,  Percentage  of  Copper 

in,  304. 

White  Metal  Smelting,  804. 
Williams',  Mr.  Lewis,  Improvements 

on  Water  Jacket,  199. 
Ziervogel,  Calcination,  160. 
Zinc  Blende  Roa-ting,  160. 
Ziervogel  Process,  327. 


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YC  63585 


